Aircraft vertical flight position display instrument

ABSTRACT

An aircraft instrument for providing a pictorial display of a vertical plane position of an aircraft, helicopter or other space operated vehicle in flight in relation to radio navigation aids or other selected reference points on the ground or in space. The instrument utilizes a computing device to establish the location of the references with respect to the vehicle in flight and the vertical pictorial display portrays the vehicle as a moving symbol, such as a red dot of light or other indicator means, positioned on a grid in a manner that shows the actual vehicle altitude above or below the reference point, distance of the vehicle from a reference point, and the vertical plane angle which would lead directly to the reference point. The instrument also includes means to provide a display of a selected or computed angular path to the same reference point so that an observer may readily determine whether the vehicle is following a proper flight path or whether it is possible to follow the proper path from the vehicle&#39;&#39;s present position in flight. Additional means are also provided in the instrument to display the relative vertical plane position of another reference point, on the ground or in space in relation to the same vertical plane by portraying the second reference point at another symbol, such as a blue dot of light or other suitable indicator means on the same grid. In the aforenoted instrument the relationships between the elements of the display is established so as to correspond to a mental image such as may be usually maintained by the pilot of the vehicle as he operates the vehicle in flight. In such manner the display serves to correlate and update the pilot&#39;&#39;s mental image with a minimum of confusion or interruptive mental action as the vehicle may rise or descend using vertical aimpoints or references.

United States Csaposs [54] AIRCRAFT VERTICAL FLIGHT POSITION DISPLAYINSTRUMENT [72] Inventor: James Csaposs, Maywood, NJ.

[73] Assignee: The Bendix Corporation [22] Filed: Aug. 14, 1969 211Appl. No.: 850,161

52 us. Cl ..340/27 NA, 343/108 511 Int. Cl ..B64d 45/00 58 Field ofSearch ..340/24, 27 NA; 343 112 PT,

FOREIGN PATENTS OR APPLICATIONS 543,638 3/1942 GreatBritain ..343/108Primary Examiner-Kathleen I-I. Claffy Assistant Examiner.]an S. BlockAttorney-Herbert L Davis and Plante, Hartz, Smith and Thompson 5 7]ABSTRACT An aircraft instrument for providing a pictorial display of avertical plane position of an aircraft, helicopter or other spaceoperated vehicle in flight in relation to radio navigation aids or otherselected reference points on the ground or in space. The instrumentutilizes a computing device to establish the location of the referenceswith respect to the vehicle in flight and the vertical pictorial displayportrays the vehicle as a moving symbol, such as a red dot of light orother indicator means, positioned on a grid in a manner that shows theactual vehicle altitude above or below the reference point, distance ofthe vehicle from a reference point, and the vertical plane angle whichwould lead directly to the reference point.

The instrument also includes means to provide a display of a selected orcomputed angular path to the same reference point so that an observermay readily determine whether the vehicle is following a proper flightpath or whether it is possible to follow the proper path from thevehicles present position in flight. Additional means are also providedin the instrument to display the relative vertical plane position ofanother reference point, on the ground or in space in relation to thesame vertical plane by portraying the second reference point at anothersymbol, such as a blue dot of light or other suitable indicator means onthe same grid.

In the aforenoted instrument the relationships between the elements ofthe display is established so as to correspond to a mental image such asmay he usually maintained by the pilot of the vehicle as he operates thevehicle in flight. In such manner the display serves to correlate andupdate the pilots mental image with a minimum of confusion orinterruptive mental action as the vehicle may rise or descend usingvertical aimpoints or references.

41 Claims, 8 Drawing Figures PRE SELAL 2 36 IIEEEIEI SCALE PATENTEDJUH 6m2 3, 668 623 SHEET 1 0F 6 -5 26 X3A37\ 8 4 200 PRE SELALT 100M w 0 39:56

FIG. 1

INVENTOR.

JAMES CSAPOSS PAIENTED JUN 6 I9I'c SHEET 30F 6 SLANT DIS IOM 820 lANNUNCIATOR LIGHTS OFFSET DISTANCE VOLTAGE T0 COM PUTER DEGREES OPERATORSELECTED NEL SW.

5 6 6 l 9 2 .I 71 x 5 E H a 1 E G C I A. M H

7 v 4 W m G M3 9 B S 9 6 k/ a a M E G M mm R 9m 6. E A w 5 G 0 am 7 A T.o O 7 TEC C. Mag 5 .A VLE I w 4 D I m ANGLE OF FLIGHTTO COMPUTER (:IXEDDESCENT ANGLE SIGNAL TO COMPUTER SELECTED 271 ALTITUDE SIGNAL TOVERTICAL NAV.

DESIRED ALT. [N

ELECTED ALJ'. BEING GREATER THAN PRESENT ALT.

AVIGATIO N CONTRO I.

PANEL FIG: 3A

Arr-a2 N5 Y PATENTEDJIIII 6 I972 3, 668 623 SHEET 5 [IF 6 s a n I I I 5as 6 449 520 l s. 447 443 J/ 479 3 44 I sIGNAL 4a) sIs l 483 450 OFFSETDIST.

4E2 I VOLTAGE 4 4 458 I NAVIGATION T 44 COMPUTER 497 499 g t- 439 437 noI 43s AGTuAL ANGLE 503 I 4ss U6 TO AIMPOINT l I 420 sIG. VOLT. GEAR I429 427 I I I OPERATOR TRAIN 42 Z SELECTED 462. I I80 A. Ex. I I sIGNALOF ACTUAL ANGLE TO I75 ANGLE OF 507 I "'I 615 AIMPOINT sIGNAL I FLIGHT-,505 r GEAR I FIXED ANGLE TRAIN *I EI IJEIJ I 5 2(3 G l T I 675 ,essGEAR I 82. 465 TRAIN Ldeso I ALTITUDE l 55 I DIFF. sIG.

e 0 672 @2226 I 670 639 I 7 643 sum sLANT DIST. TO

I AIMPOINT sIG. I voLTAGE I I44 J90 I SELECTED 78o I ALT. SIG.

sIGNAL-HIGH I I43 VOLTAGE y slGuAL- MEDIUM ggr; F ,9 873 1 ALT. CAPTURESIGNAL FROM COMPUTER LOGIC CLIMB SIGNAL FROM COMPUTER LOGIC INVENTOR.

ATTORNEY PATENTEDJUM 6I972 SHEET 80F 6 DESCENT SITUATION ACTUAL DISTANCETo SPACE POI (WAYPOINT) VEHICLE STARTING i ALTITUDE SELECTED ACTUALFLIGHT PATH ANGLE TO ANGLE SPACE POINT I FIG:4

WAYPOINT &

PRE- SELECTED ALTITUDE CLIMB SITUATION I AcTuAL DISTANCE TO sPAcE POINT(WAYPOIN'I') ALTITUDE DIFFERENCE ACTUAL ANGLE TO SELECTED 'Z,",$ VEH|CLEFLIGHT PATH STARTING ANGLE ALTITUDE FIG:5

WAYPOINT I,

:IMPOINT FIRE-SELECTED ALTITUDE EARTH OFFSET DESCENT SITUATION FIG: 6

WAY PO I NT ACTUAL DISTANCE TO WAYPOINT ACTUAL DISTANCE TO OFFSETAIMPOINT DISTANCE VEHICLE I INT STARTING A MP0 ALTITUDE i SELECTEDAcTuAL FLIGHT PATH ANGLE To ANGLE AIMPOINT PRE-SELECI'E D ALTITUDE I/////////////////EARTH///////////// 1fi\/ENTQR JAMES CSA POSS BY zATTORNEY AIRCRAFT VERTICAL FLIGHT POSITION DISPLAY INSTRUMENT CROSSREFERENCE TO A RELATED APPLICATION The present application relates to animproved compact display instrument of a type such as described andclaimed in a copending U. S. application, Ser. No. 548,550 filed May 9,1966 by Richard L. Cohen for AN AIRCRAFT FLIGHT POSITION DISPLAYINSTRUMENT, now U.S. Pat. No. 3,505,640, granted Apr. 7, 1970 to RichardL. Cohen and assigned to The Bendix Corporation, assignee of the presentinvention.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to a field in which increasing traffic congestion of certain airspaces near principle airports and the requirements for more accuratecontrol of aircraft vertical o erations to improve performance have ledto a need for systems to provide more comprehensive vertical control ofair-borne vehicles. In order to maintain proper control, monitorautomatic flight control systems and operate more efficiently in controlzones, it is necessary that the operator know the vehicles presentposition, intended flight path, progress at all times and its capabilityto conform to a controllers request. Although heretofore many pictorialand map displays have been developed for portraying the horizontalposition of an aircraft in flight over the earths surface, an entirelysatisfactory means for displaying the vertical location and path of sucha flying vehicle has not been produced. The aircraft vertical flightposition display instrument of the present invention, satisfies thisneed of the operator for vertical situation information with a complete,compact and easy to interpret display presentation.

2. Description of the Prior Art Heretofore means have been utilized togenerate grid and moving spots required to display the aircraft andreference points, including the use of cathode ray tube devices withgrid and symbol painting control circuits. The present inventionutilizes an electro mechanical optical means of generating the movingsymbols on a grid glass which may be small enough to be used on the faceof an aircraft panel instrument.

In carrying out the present invention, there may be utilized an idea ofmeans described and claimed in the aforenoted copending US. Pat. No.3,505,640, granted Apr. 7, 1970 to Richard L. Cohen for generatingindicating dots to represent the position of an aircraft in flight inrelation to a reference point.

However the visual display instrument of the last mentioned U.S. Pat.No. 3,505,640, includes a control means for receiving distance andbearing signals from a facility for transmitting such signals to operatethe display dot generating means and in no sense, suggests the controlmeans of the present invention for providing a display of the verticalplane position of the aircraft in flight.

The use of the display dot generating means, together with the controlmeans of the present invention, permits the instrument case to be ofsize that may be conveniently mounted along with other flightinstruments on the instrument panel of a vehicle and which verticaldisplay may be observed by the operator without engaging in large eye orhead movements away from the primary flight instruments.

SUMMARY OF THE INVENTION The present invention relates to a compactaircraft vertical flight position display instrument in which therelationship between a grid and reference symbol of the instrumentcorrespond closely to a mental picture (or image) as it exists in theaverage pilots mind. The display arrangement is such that it may beinterpreted rapidly and accurately by a pilot without new instrumenttraining or extensive practice in the interpretation of display data.

An object of the invention is to provide a vertical plane displayinstrument corresponding to the plane which passes through a verticalline erected at the horizontal reference point on the earth surface andpasses through the point corresponding to the vehicle's actual positionin space.

Another object of the invention is to provide a display instrumentutilizing a grid in the instrument to show the relationship of a vehiclein flight to its vertical aimpoint (destination) and referencednavigation aids.

Another object of the invention is to provide a rotating or movingcursor to describe the best or desired vertical path of the vehicle inflight to a reference point.

Another object of the invention is to provide a vertical grid and anumerical display to portray the selected or directed altitude of theactual vehicle flight position in relation to the selected altitude,either above or below.

Another object of the invention is to provide moving symbols on a gridto display and calibrate the vertical plane relationship between avehicle in flight and its intended space destination and therelationship of both to another reference such as a radio aid.

Another object of the invention is to provide grid line identificationsand annunciator devices that permit changing of scales without affectingthe most significant number.

Another object of the invention is to provide a two sided symmetricalgrid so arranged that the display maintains a valid relationship whenthe aircraft has passed the reference point and has proceeded withfurther maneuvers such as an approach to the destination field.

Another object of the invention is to provide an idea of means such asdescribed and claimed in the aforenoted US. Pat. No. 3,505,604 forgenerating two colored dots on an instrument display, but which idea ofmeans as applied in the present invention is distinguished from that ofthe aforenoted US. Pat. No. 3,505,640 in that the display is effectivelycontrolled so as to provide a continuously updated vertical picture ofan aircraft or vehicle location in flight and the location of a selectedreference with respect to a navigation reference such as a VORTACstation.

Another object of the invention is to provide effective horizontal andvertical scales on a grid so arranged that both may be changed togetherto produce a constant angular relationship for the flight path or actualangle of flight of the aircraft to an aimpoint.

Another object of the invention is to provide means to effect verticalplane angular bearing and distance to a desired vertical destinationpoint (aimpoint) and to position an aircraft symbol on a verticalsituation display.

Another object of the invention is to provide means to effect verticalplane height above or below a desired vertical destination (aimpoint)coupled with the horizontal distance from the destination and toposition a vehicle symbol on a ver tical situation display.

Another object of the invention is to provide means to effect an offsetdistance (distance between waypoint destination and aimpoint) and toposition a symbol on the vertical situation display to depict analternate reference point.

Another object of the invention is to provide means to effect an offsetdistance and offset altitude and to position a symbol on a verticalsituation display so as to depict an alternate reference point.

Another object of the invention is to provide means to effect a verticaldisplay so as to pictorially verify for the operator the flight pathangle he has selected, the altitude he has selected, and to immediatelydisplay to the operator his capability of conforming to his selection.

Another object of the invention is to provide means of programming anddisplaying a selected angle of climb or descent, or by operation of asimple selection switch obtain a preselected descent angle or a cruiseclimb command automatically, depending on the altitude selection aboveor below the starting vehicle altitude.

Another object of the invention is to provide an aircraft verticalflight position display instrument in which the vertical plane displayedby the instrument is such that if the aircraft is not on a directgeometric course to the reference point, the vertical plane displayedwill continuously change to correspond to the new space position of thevehicle.

Another object of the invention is to provide such a display instrumentin which so long as the vehicle has a component of velocity in thedirection of the reference point, the vehicle symbol will move to theright, i.e. regardless of the compass orientation of the vertical plane,the display will be operating from left to right, but the controlarrangement is such that after passing the reference point, the vehicleassembly will continue to the right to maintain the same image of thevertical plane displayed.

Another object of the invention is to provide an aircraft verticalposition display instrument which efiects a complete, compact, easy tointerpret presentation of the vertical situation information.

These and other objects and features of the invention are pointed out inthe following description in terms of the embodiment thereof which isshown in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS In the drawings in which corresponding partshave been indicated by corresponding numerals.

FIG. 1 is a front view of a vertical pictorial display instrumentembodying the present invention and showing a fixed grid with a centerreference point and scaled numbers, a moving cursor indicating a desiredangular flight path, an aircraft light indicator dot, a referencestation light indicator dot, a selected altitude hold flag andannunciator numbers which show the active scale of the presentation.

FIG. 2 is a side view of the display instrument of FIG. 1 with certainparts broken away so as to better illustrate the instrument bezel, facemask, the grid screen, rotating cursor disc and four discs forgenerating the indicator light dots.

FIG. 3A illustrates diagrammatically a navigation control panel of aflight vehicle interconnected with portions of a block diagram shown byFIGS. 3A, 3B and 3C of an electromechanical optical implementation ofthe operative mechanism of the display instrument of FIGS. 1 and 2.

FIG. 3B illustrates diagrammatically a vertical pictorial displayindicator interconnected with portions of the block diagram shown byFIGS. 3A, 3B and 3C of the electromechanical optical implementation ofthe display instrument of FIGS. 1 and 2.

FIG. 3C illustrates diagrammatically a navigation computer of a flightvehicle interconnected with portions of the block diagram shown by FIGS.3A, 3B and 3C of the electromechanical implementation of the displayinstrument of FIGS. 1 and 2.

FIG. 4 is a graphical presentation of a descent situation and theimplemented geometry displayed by the instrument of the presentinvention under such operative conditions of the aircraft.

FIG. 5 is a graphical presentation of a climb situation and theimplemented geometry displayed by the instrument of the presentinvention under such operative conditions of the aircraft.

FIG. 6 is a graphical presentation of an offset descent situation andthe implemented geometry displayed by the instrument of the presentinvention under such operating conditions of the aircraft.

DESCRIPTION OF THE INVENTION Referring to FIGS. 1 and 2, referencenumeral 10 indicates a casing of the display instrument having a rearelectrical connector 12 and a front bezel 14 and within which casing isprovided the operating mechanism of the display instrument, ashereinafter explained.

The front bezel 14 includes a wedge shaped face glass 16 which seals thecasing 10 while allowing a view of the internal pictorial elements andmechanisms.

The operating mechanism of the display instrument of FIGS. 1 and 2,including the gearing and electromechanical servo elements showndiagrammatically in FIGS. 3A, 3B and 3C, are contained within the casing10 and attached by a mechanism plate 20 and mounting posts 22 to thebezel 14, as a complete assembly, as best shown in FIG. 2.

The electronic elements shown diagrammatically in FIGS. 3A, 3B and 3Care mounted behind the mechanism and within the casing 10 and furtherare connected by suitable electrical conductors to the mechanism andface elements, as shown by the broken away portions of FIG. 2.

As best shown in FIG. 1, at the two upper corners of the bezel 14 arelight wells which contain small electrical bulbs 23 and 25 forilluminating the face glass 16 by reflection off of wedge taperedsurfaces of the face glass 16 in a conventional manner, as illustrateddiagrammatically in FIG. 38.

Further fixed to the mechanism plate 20 by suitable mounting posts, oneof which is indicated in FIG. 2 by the numeral 27, is an opaque mask 29having an opening 30 therein. Fastened directly behind the mask 29 andexposed through the opening 30 is a clear glass disc 31 which is securedto the mask 29 by suitable means to provide a display plate.

The clear glass disc 31 has a grid 32 and grid scales 33 etched on itssurface as well as an instrument center point 35 representing theaimpoint, a horizontal grid center line 28 which extends from the leftand right sides of the center point 35, and a grid vertical center line26 which extends from above and below the center point 35. These indiciashow through the face glass 16 and the opening 30 in the opaque mask 29,as shown in FIG. 1. The flight path angle index 34 and other numericalsymbols and letterings are painted on the surface of the opaque mask 29and are also viewable through the face glass 16, as best shown in FIG.1.

Windows 34A, 36, 38 and 40 are provided in the mask 29 to allow viewingtherethrough of annunciator lights 35, 37, 39 and 41 which are fastenedto the back of the mask 29. Illumination of these lights may beeffectively controlled, as shown diagrammatically in FIG. 3A.

A window 43 is also provided at the lower portion of the mask 29 so thatnumerical lamps 45 may be selectively illuminated so as to displaytherethrough a selected altitude, as hereinafter explained withreference to the diagrammatic drawing of FIG. 3A. Shown at the top ofthe mask 29 is another window 48 through which may be viewed an altitudehold flag spade 49 which may be actuated so that it either shows throughthe window 48 or disappears from view by the operation of suitableelectromagnetic actuating means, as hereinafter explained with referenceto the diagrammatic view of FIG. 38.

Furthermore a shouldered shaft 50 is mounted on the mechanism plate 20,as shown in FIG. 2, in a position in alignment with the center point 35of the grid 32 etched on the clear plate 31, as indicated in FIG. 1.Suitable glass discs 53, 55, 57, 58 and 60 are freely mounted on reduceddiameters of the shaft 50, as best shown in FIG. 2.

Each disc has a metal bearing fastened into a center hole and a rim gearfastened to its outer edge, and while disc 55, as shown in FIG. 3B, isinitially fixedly positioned, the remaining discs 53, 57, 58 and 60 arefree to be rotated independently of each of the other discs. The discs53, 57, 58 and 60 are in mesh with drive pinions, as showndiagrammatically by FIG. 3B, which in turn are mounted on shafts whichextend out from the operating mechanism. These shafts extend through themechanism plate 20 of FIG. 2 so that each of these discs may be rotatedto various positions determined by the operating mechanism.

The front disc 53 is formed of a clear glass and has a flight pathcursor line 61, etched along a radial line from the center of the disc53 which corresponds to the center line of the shaft 50 in alignmentwith the center point 35 etched on the clear glass disc 31 and viewablethrough the window 16, as shown by FIG. 1. The discs 55, 57, 58 and 60may be physically constructed in a like manner to that of the red andblue colored discs arranged as heretofore described and claimed in theaforenoted US. Pat. No. 3,505,640. The discs 55, 57, 58 and 60 may beprovided in a somewhat similar arrangement to effect an aircraftposition indicator dot 75 and waypoint indicator dot 77.

Moreover immediately behind the last rotating glass disc 60 is located alight cup 62 carrying several incandescent electric light bulbs whichmay be suitably illuminated as indicated diagrammatically in FIG. 3B.The cup is of a size corresponding to the disc 60 and has a hole in thecenter to allow the shaft 50 to pass therethrough. The shaft 50 isfastened to the mechanism plate 20.

The discs 55 and 57 may be formed of a suitable colored glass, such as ared glass, with a suitable radial slot being provided in the disc 55 anda suitable Archimedian spiral slot being provided in the disc 57.

The discs 58 and 60 may be formed of a suitable different colored glass,such as a blue glass; with a suitable radial slot being provided in thedisc 58 and a suitable Archimedian spiral slot being provided in thedisc 60.

The operative arrangement of the discs 55, 57, 58 and 60 is such that avariably positioned beam of light indicative of the flight position ofthe vehicle or aircraft is viewable on the grid 32 through the window 16of the display instrument as a red dot 75, as shown by way of example byFIG. 1.

The red dot 75 indicative of the vehicle or aircraft position isproduced on the face of the instrument when the white light from thelight cup 62 passes through the intersection of the clear Archimedianspiral slot of blue disc 60 and the clear radial slot of blue disc 58and then in turn passes through the red colored portions of red disc 57and red disc 55. The observer at the front of the instrument sees thebeam formed by the intersection of the slots as a bright red dot 75which is the same shape as the geometric shape formed by the linesdefining the sides of the clear spiral slot in the blue disc 60 and theclear radial slot in the blue disc 58. Light that passes through thecolored portion of one or both blue discs as well as both red discs isvery dim in contrast with the light which has passed through the clearportions of the blue disc and the colored portion of both red discs asin the disclosure of the aforenoted US. Pat. No. 3,505,640.

Thus the red dot 75 may be effectively generated by the adjustedpositions of the discs 58 and 60.

On the other hand in those cases in which the waypoint, as indicatedgraphically by FIG. 6, is different from that of the aimpoint 35, theposition of the waypoint is indicated on the grid 32 of the displayinstrument by a beam of light which passes through the portion of thespiral slot in the red colored disc 57 which coincides with the radialslot in the red disc 53, so that a portion of the white light passingthrough the blue discs 60 and 58 will then pass through the small clearopening formed by the intersections of the slots of the discs 57 and 55and will appear to the observer at the front of the device to be a bluedot 77 of light on the grid 32 with a geometric shape defined by theedges of the radial slot in the red disc 55 and the spiral slot in thered disc 57. The remaining blue light passing through the red coloreddiscs 55 and 57 will be filtered until it is dim in comparison to theblue dot 77 indicative of the waypoint.

The operating mechanism for the display instrument, as showndiagrammatically in FIGS. 3A, 3B and 3C, include conventional gears,differentials, shafts, bearings, motors and rotating potentiometers toprovide the four servo systems to position the light dot control discs57, 58 and 60, as well as the cursor line control disc 53 in response tofunctional signals for angular bearings and distances representing thevertical position location of the vehicle or aircraft in flight andrelative location of the navigation aids or reference points.

OPERATING MECHANISM OF FIGS. 3A, 3B and 3C The operating mechanism forthe display instrument 10 of FIGS. 1 and 2, as shown diagrammatically inFIGS. 3A, 3B and 3C, includes a navigation control panel operativelyconnected to a navigation computer and to the display instrument 10which is in turn operatively connected between the control panel 100 andcomputer 1 10.

The navigation computer 1 10 may be of a conventional ty e or thecomputer 110 may include a system for controlling an aircraft to attaina predetermined altitude such as described and claimed in a US. Pat. No.3,545,703, granted Dec. 8, 1970 to Jerry Doniger and Joseph H.McLaughlin on a U.S. application, Ser. No. 679,757, filed Nov. 1, 1967and assigned to The Bendix Corporation.

In the operation of the foregoing display instrument 10, an operator orpilot of an aircraft carrying the display instrument, determines a pointin space (waypoint) that he intends to use as a destination point (seethe graphical illustrations of FIGS. 4, 5 and 6).

In order to determine this destination point with respect to the displayinstrument 10, the operator defines its location in space in terms ofaltitude above ground level, indicated graphically in the FIGS. 4, 5 and6 by the legend pre-selected altitude. The pilot or operator selects thenavigation fix (radio station or ground point) which he intends toapproach. A navigation computer (not part of this invention) byconventional geometric computing means determines the actual distancefrom the vehicle in flight to the space point and the actual angle tothe space point, as indicated by the legends of FIGS. 4, 5 and 6, andfurther the operator determines the vertical path along which he wishesto approach the waypoint in the flight of the aircraft in terms of theselected flight path angle as indicated by such legends on the graphicalillustration of FIGS. 4, 5 and 6. Thus it will be seen that thehorizontal path is the pilots selected flight track and the verticalpath is the pilots selected flight path angle".

In the type of system herein described, a point on the earth s surfacecorresponding to that of the waypoint may in efiect be a VORTACnavigation transmitter of conventional type, a VORTAC transmitter, or apoint defined by an airborne inertial platform or navigation computer oftypes well known in the art. Moreover other conventional means, such asa course line computer of a type well known in the art, may be utilizedto compute the horizontal distance and true bearing of this point on theearths surface.

Referring now to FIGS. 1, 3A, 4, 5 and 6 the vertical situation of thewaypoint in space is set up for display on the instrument 10 by theoperator selecting the desired altitude of the space or waypoint by anappropriate adjustment of an altitude selector knob provided on thenavigation control panel 100. The altitude selector knob 115 ismechanically connected by suitable operating means 1 17 to an altitudecounter 118 of conventional type provided on the control panel 100. Thecounter 1 18 is adjusted then by an operator adjustment of the knob 115so as to read the desired altitude of the waypoint.

Such adjustment of the knob 115 simultaneously elfects a correspondingadjustment through the operating means 1 l 7 of an encoder 119 ofconventional type and arranged to convert the altitude displayed by thecounter 45 to a BCD code for each digit. These electrical digit codesignals are applied by the encoder 119 through a grounded outputconductor 121 and through an output conductor 123 connected across aninput to a numerical lamp device 45 also of a conventional type andarranged to repeat (reproduce) the numbers displayed by the counter 118.

There is also operatively connected to the altitude selector knob 115 bythe operating means 117 an arm 125 variably contacting a resistorelement 126 of an analog device or potentiometer 127 arranged to produceacross a grounded input-output conductor 129 and an output conductor 131leading from the arm 125 an electrical output signal which isproportional to the altitude selected by the operator-operativeadjustment of the knob 1 15. The variable resistor element 126 of thepotentiometer 127 is connected by the grounded input conductor 129 andan input conductor 133 across a source of alternating current 135 i.e.output terminal 137 and grounded terminal 139 thereof). The alternatingcurrent applied across the terminals 137 and 139 is of a phase whichlags by 180 a phase of an alternating current of like frequency suppliedby the same source 135 across output terminals 139 and 141.

The alternating current signal voltage applied then across the outputconductors 129 and 131 of the potentiometer 127 is transmitted to inputterminals 143 and 144 of the navigation computer 110, showndiagrammatically by FIG. 3C. This signal voltage is utilized in thecomputer 110 to provide control signals to operate suitable means tocontrol the flight of the aircraft. The computer 110 may be of a typefor controlling flight of an aircraft to attain a predetermined altitudeand may be of a. conventional type or of a type such as described andclaimed in the aforenoted US. Pat. No. 3,545,703.

The electrical signal proportioned to the selected altitude appliedacross the input terminals 143 and 145 of the navigation computer 1 iscompared in the computer 110 to a voltage signal corresponding to theactual altitude of the aircraft in flight and to another voltage signalcorresponding to the distance of the selected point on the earthssurface obtained from a horizontal computer. From this geometriccomparison (see the graphical illustrations of FIGS. 4, 5 and 6) threefactors for use by the display instrument are derived; l the differencein altitude between the desired altitude and the actual altitude of theaircraft; (2) the actual angle to the aimpoint or space point which maybe positive or negative; and (3) a climb signal in the event theselected altitude is above the actual or prevailing altitude of theaircraft in flight, as will be explained hereinafter in greater detail.

Flight Path Angle In the system herein described, the operator in theselection of the flight path angle has two choices provided for controlof the vehicle and these in turn effect the operation of the displayinstrument 10. These choices may be efi'ected by the operator setting ofa selector switch 145 provided on the navigation control panel 100 andselectively operated by the operator, as hereinafter described, so thatthe operator may select the angle at which it is desired to climb ordescent, or there may be alternately effected operation of a preselecteddescent angle or a preselected cruise climb control effected by computermeans based on flight parameters such as airspeed and/or mach number.

It will be seen from the diagrammatic view of FIG. 3A that the operatormay selectively position the switch 145 so as to alternately open andclose switch contacts 147 and 149. The switch contact 147 is connectedby an electrical conductor 151 to an arm 153 of a potentiometer 155having a resistor element 157 adjustably contacted by the potentiometerarm 153. The adjustable resistor 157 has a grounded center tap 159, oneend of the resistor element 157 is connected by a conductor 161 to theelectrical conductor 163 leading to the terminal 137 of the source ofalternating current 135, while an opposite end of the resistor element157 is connected by a conductor 162 and 164 to the terminal 141 of thesource of alternating current 135. The source 135 applies an alternatingcurrent voltage across the grounded center tap 159 and the conductor 161of a phase which lags by 180 the phase of the alternating currentvoltage applied across the terminals 139 and 141 of the source ofalternating current 135. Both alternating current voltages being of alike frequency.

The arm 153 of the potentiometer 155 is adjustably positioned inrelation to resistor 157 and selectively at opposite sides of thegrounded center tap of the potentiometer 155 by an operatonoperativeflight angle selector knob 165. The knob 165 is drivingly connectedthrough suitable means 167 to the adjustable potentiometer arm 153 and acounter mechanism 169 of a conventional type arranged to show thepositive or negative flight path angle desired dependent upon theadjustment of arm 153 in relation to the grounded center tap 159. Theadjustable arm 153 of the potentiometer is thus operatively connected bythe means 167 to the flight angle selector knob and the counter 169.

The arrangement is such that the potentiometer 155 produces an outputvoltage proportional to the position of the counter 169 as effected bythe operation of the flight angle selector knob 165 by the operator. Theflight angle output voltage of a selected phase and magnitude is appliedacross the grounded output conductor 159 and a conductor 171 leadingfrom the output conductor 151 of the potentiometer 155 to a inputterminal 175 of the navigation computer 110, as shown by FIG. 3C.

This voltage applied at the input terminal 175 of the navigationcomputer 110 is utilized by suitable means provided in the navigationcomputer 110 to compute control signals applied to suitable controlmeans of the aircraft to cause the aircraft to follow a selected flightpath in a conventional manner.

Further there is connected across the conductors 161 and 162 leadingfrom the opposite ends of the resistor element 157 of the potentiometer155 a second resistor element 177 of a potentiometer 179 having agrounded center tap 181. The potentiometer 179 has an adjustablepotentiometer arm 183 arranged to variably contact the resistor element177. The potentiometer arm 183 is electrically connected by a conductor185 to one terminal of a primary winding 187 of a coupling transformer189 while an opposite terminal of the winding 187 is connected by aconductor 191 to the switch arm 145. Thus upon the switch arm 145closing the contact 147 the conductor 191 will in turn be connectedthrough conductor 151 to the potentiometer arm 153 which variablycontacts the resistor element 157 of the potentiometer 155.

It will be seen from the foregoing arrangement, as showndiagrammatically by FIG. 3A, that the potentiometers 155 and 179 providea balancing bridge circuit effective upon the switch arm 145 closing thecontact 147 to apply upon the potentiometers 155 and 179 being in anunbalanced relation, an alternating current voltage through the primarywinding 187 which output voltage will be induced through the couplingtransformer 189 to a secondary winding 193 thereof. The secondarywinding 193 has one end grounded at 195 and an opposite end connectedthrough a conductor 197 to an input terminal 199 of a servo amplifier201 of a conventional type having a grounded input-output terminal 203.

Further an output terminal 205 of the amplifier 201 is connected througha conductor 207 to one terminal of a control winding 209 of aconventional two phase servomotor 21 1. The servomotor 211 has a fixedphase winding 213 having one terminal thereof connected together with aterminal of the control winding 209 to a grounded conductor 215. Anopposite terminal of the fixed phase winding 213 is connected through aconductor 217 to the conductor 161 which in turn leads through theconductor 163 to the output terminal 137 of the source of alternatingcurrent 135.

The servomotor 211 drives through an output shaft 219, gear train 221and shaft 223, a shaft 225 which is in turn drivingly connected to thearm 183 of the position follow up potentiometer 179. The arm 183 isdriven by the servomotor 21 1 so as to vary the resistor element 177 ofthe potentiometer 179 in a sense dependent upon the electrical unbalancerelation of the bridge circuit which in turn effects an alternatingcurrent error voltage applied through the coupling transformer 189 so asto cause the motor 211 to drive the arm 183 in a sense to balance theopposing voltages and effect a null output error voltage at the outputcoupling transformer 189. The shaft 225 further drives through a pinion227, as shown diagrammatically by FIG. 3B, to angularly position theflight path angle cursor disc 53.

It will be seen then that upon the operator selectively positioning thepanel switch 145 so as to close the switch contact 147, a voltage willbe transmitted by the potentiometer 155 to the signal output transformer189 where it is compared with an opposing voltage produced by thepotentiometer 179. The arm 183 of the potentiometer 179 is adjustablypositioned by the servomotor 21 1 to an angular position dependent uponthe angular position of the flight path angle cursor disc 53 effected bythe servomotor 211 through the gearing 221 and shaft 225. Thepotentiometer 179 produces then an output voltage proportional to theangle between the cursor and the horizontal center line 28 of thedisplay instrument.

Thus if the cursor disc 53 does not display the same angle as that shownon the counter 169 which reflects the adjusted position of thepotentiometer arm 153 of the potentiometer 155 effected by the manuallyoperable knob 165, the arrangement is such that the coupling transformer189 induces an error voltage into the secondary winding 193 of thecoupling transformer 189 which is applied to the servo amplifier 201 soas to cause the servomotor 211 to effect a corresponding angularadjustment of the flight path angle cursor disc 53 until it ispositioned to an angle such that its position when read on the flightpath-index 34 of the display instrument of FIG. 1 will be the same asthat displayed by the counter 169 of the navigation control panel 100 ofFIG. 3A.

Upon the foregoing conditions being established, voltage of the twopotentiometers 155 and 179 will be the same and the servo control systemof the motor 211 for angularly positioning the flight path angle disc 53will be at a null. The cursor line 61 on the disc 53 will then showthrough the grid 32 etched on the grid glass disc 31 of FIGS. 1 and 2 tovisually indicate to the operator the angle of the selected flight pathof the aircraft to the aimpoint, represented by the center point 35 ofthe grid 32.

Now should the operator alternately set the panel selector switch 145 soas to open the switch contact 147 and close the switch contact 149, hewould thereby bring into effect one of two fixed commands for thevertical navigation computer 110 of FIG. 3C and the display instrumentof FIGS. 1 and 2.

Moreover upon no climb signal being applied through an output conductor250, a selector relay 257 will be effectively deenergized. The outputconductor 250 leads from an output terminal 252 of a computer logiccircuitry provided in the navigation computer 1 to a control winding 254of the relay 257 having a grounded terminal 255.

A fixed resistor network 261 will then upon the deenergization of therelay 257 produce a predetermined control voltage equivalent to a fixeddescent angle preselected for the control of the aircraft under suchconditions. The predetermined voltage provided by the resistor network261 thereupon acts to control operation of the flight path angle servoincluding the coupling transformer 189, servo amplifier 201 andservomotor 211 which responds to the signal voltage supplied by thefixed resistor network 261 so that the cursor disc 53 will be angularlypositioned by the servomotor 211 to a position corresponding to thepre-set angle represented by the resistor network 261.

The fixed resistor network 261 includes resistor elements 263 and 265serially connected by a conductor 267 and having an end of the resistor263 connected by a conductor 269 to an end of the resistor element 157and to the conductor 162 leading through conductor 164 to the terminal141 of the source of alternating current 135. An opposite end of theresistor 265 is connected to a grounded conductor 271.

In the aforenoted arrangement of the fixed resistor network 261 aconductor 273 leads from the switch contact 149 selectively closed bythe switch arm 145 to a relay switch element 275 normally biased underspring tension into a position to close a relay contact 277 connected bya conductor 279 to the conductor 267 serially connecting the resistorelements 263 and 265. Also leading from the conductor 273 and the switchcontact 149 closed by the selector switch 145 is an output conductor 281to apply under such operating conditions a fixed descent angle signalvoltage to an input temiinal 283 of the navigation computer 110,illustrated diagrammatically by FIG. 3C. The fixed descent angle signalvoltage acts through the navigation computer to compute control signalsfor suitable control means of the aircraft to cause the aircraft inflight to descend at said fixed angle.

However upon the altitude selected by the operator by adjustment of thecontrol knob being greater than the prevailing or present altitude offlight of the aircraft, the computer logic circuitry of the navigationcomputer 1 10 applies an output voltage at the terminal 252 which is inturn applied through the conductor 250 to energize the control winding254 of the relay 257 which in turn applies a magnetic force to actuatethe relay switch arm 275 to open the relay switch contact 277 and closea second relay contact 287 connected to the grounded conductor 255 whichin turn shorts the fixed resistor network 261 out of operation It willbe seen then that upon a climb signal being applied by the navigationcomputer 110 to the relay 257 as upon the selected altitude beinggreater than the prevailing altitude of flight of the aircraft, therelay 257 will thereupon cause the circuit to the output signaltransformer 189 to be grounded so that unless the servomotor follow uppotentiometer 179 be centered at which the potentiometer arm 183 will beconnected directly to the grounded conductor 181, there would beeffected an output voltage signal at the coupling transformer 189 whichwould cause the servomotor 211 to adjust the potentiometer arm 183 in asense to the center or null signal position. The flight path angleservomotor 211 would thereupon cause the disc 53 to be so angularlyadjusted that the cursor line 61 on the disc 53 would be aligned withthe horizontal center line 28 on the grid of the transparent disc 31 ofFIG. 1 and which would then represent to the operator a zero flight pathangle. Such zero angle indication would thereupon provide a visualcommand signal to the operator for an immediate maximum climbperformance (based on time or fuel) of the aircraft to the selectedaltitude by appropriate pilot operation.

OFFSET NAVIGATION AID POSITION (WAYPOINT INDICATOR DOT 77) Under manyoperating conditions of the aircraft the aimpoint and waypoint, asindicated graphically by FIGS. 4 and 5, may in effect be at the samepoint. However, under other operating conditions, as indicatedgraphically in FIG. 6, the vehicle or aircraft operator may desire toachieve the preselected altitude at some distance (offset) before hereaches the selected waypoint and under the latter operating conditionshe must in effect establish a new point in space as the aimpoint. Thenew aimpoint, under such circumstances, as indicated graphically in FIG.6, being at the same altitude originally selected, as indicated at 45 ofFIGS. 1 and at 118 and 45 of FIG. 3A, and would be located along thepreviously selected horizontal approach track at a distance from theoriginally selected waypoint equal to the offset distance. Since thisnew aimpoint, as indicated graphically in FIG. 6, would be the primarytarget of the vehicles vertical maneuver, the center point 35 of thegrid 32 of FIG. 1 will still represent the aimpoint, while a blue dotindicated by way of example in FIG. 1 by the numeral 77 will representon the display instrument the waypoint shown graphically in FIG. 6.

Inasmuch as the actual vertical plane angle between the aimpoint and thewaypoint shown graphically by FIG. 6 is zero under the supposedoperating conditions, it will be seen that the red disc 55 shown in FIG.38 will be fastened in a fixed position with the radial slot providedtherein aligned with the horizontal grid center line 28 extending fromthe right side of the center point 35. Moreover since in theimplementation of the invention described herein the vertical display ofthe instrument of FIG. 1 is intended only to show the offset distancewhen the aimpoint and waypoint are at the same altitude no servomechanism has been provided for angularly positioning the red disc 55with the radical slot provided therein.

It should be noted however that if capability for computing an offset inaltitude as well as in distance is desired and included in thenavigation computer 110, the actual angle to the offset point orwaypoint would be computed and used to control suitable servomotor meansto angularly position the red disc 55 and the angular position of theradial slot therein accordingly.

In the present embodiment of the invention, the offset distance isselected by the vehicle operator making an appropriate adjustment of anoffset distance selector knob 300 provided on the navigation controlpanel 100. The offset distance selector knob 300 is mechanicallyconnected by suitable operating means 303 to an offset distance milescounter 305 of conventional type provided on the control panel 100. Thecounter 305 is adjusted then by an operator adjustment of the knob 300so as to read the desired distance in miles of the waypoint from theaimpoint or offset distance" as shown graphically by FIG. 6.

Such adjustment of the knob 300 simultaneously efiects a correspondingadjustment through the operating means 303 of an arm 307 variablycontacting a resistor element 308 of a potentiometer 309 arranged toproduce across a grounded input-output conductor 311 and an outputconductor 313 leading from the arm 307 an electrical output signal whichis proportional to the offset distance selected by the operatoroperativeadjustment of the knob 300. The variable resistor element 308 of thepotentiometer 309 is connected to the grounded input conductor 31] andby an input conductor 315 to the conductor 163 and thereby across anoutput terminal 137 and grounded terminal 139 of the source ofalternating current 135.

The operator-operative selected adjustment of the knob 300 and therebythe potentiometer arm 307 of the potentiometer 309 effects analternating current output voltage across the output lines 311 and 313which represents the selected offset distance". This alternating currentoutput signal voltage applied then across the output conductors 31 1 and313 of the potentiometer 309 is transmitted to input terminals 145 and320 of the navigation computer 110, shown diagrammatically by FIG. 3C,and which output signal voltage is utilized in the navigation computer110 to provide control signals for operating suitable means to controlthe flight of the aircraft.

This offset distance" signal voltage is also applied through a conductor323 leading from the potentiometer arm 307 to one terminal of a primarywinding 325 of a coupling output signal transformer 327. The oppositeterminal of the primary winding 325 is connected by a conductor 329 toan adjustable arm 331 variably contacting a resistor element 333 of afollow up position potentiometer 335. One terminal of the resistorelement 333 of the potentiometer 335 is connected to a groundedconductor 337 while an opposite terminal of the resistor element 333 isconnected through a conductor 339 to a switch arm 341 of a slantdistance excitation control relay 345.

The relay switch arm 341 of the relay 345 is normally biased underspring tension into a contacting relation with a relay contact 347connected by an electrical conductor 349 to a relay switch arm 351 of asecond slant distance excitation control relay 355. The relay switch arm351 is normally biased under spring tension into contacting relationwith a relay contact 357 connected by an electrical conductor 359 to aterminal 361 of the source of alternating current 135.

The source of alternating current 135 has in addition to the outputterminal 361 other output terminals 363 and 365. The source ofalternating current 135 is arranged to apply across the groundedterminal 139 and the terminal 361 an alternating current voltage of arelatively low amplitude while across the grounded terminal 139 and theterminal 363 there is applied an alternating current voltage of arelatively medium amplitude and across the grounded output terminal 139and the output terminal 365 there is applied an alternating currentvoltage of a relatively high amplitude.

These alternating current voltages of relatively low, medium and highamplitudes are of a same phase and frequency as that of the alternatingcurrent voltage applied across the grounded terminal 139 and the outputterminal 137 of the source of alternating current 135.

Moreover these alternating current voltages of high, medium and lowamplitudes are controlled by the respective slant distance excitationcontrol relay 345 and 355 and are so arranged as to change theinstrument scaling automatically as the vehicle comes within the rangeof the larger (more sensitive) scales as hereinafter described ingreater detail.

It is sufi'rcient to say for purpose of the present explanation that theslant distance alternating current excitation applied then through theconductor 339 and grounded conductor 337 across the resistor element 333of the position follow up potentiometer 335 is applied through theoutput conductor 329 to the primary winding 325 of the signal couplingtransformer 327 so as to act in opposition to the voltage applied by theoffset distance potentiometer 309.

A resultant difierence between the compared alternating current signalsapplied to the primary winding 325 will then induce an error signal in asecondary winding 375 of the coupling transformer 327. Secondary winding375 has one terminal connected to a grounded conductor 377 and anopposite terminal connected through a conductor 379 to an input terminal381 of a servo amplifier 383 having a grounded input-output conductor385. The servo amplifier 383 has an output terminal 387 from which leadsan output conductor 389 to one terminal of a control winding 391 of atwo phase servomotor 395 having a fixed phase winding 397. One terminalof the fixed phase winding 397 is connected through the conductor 399 tothe conductor 161 and thereby through conductor 163 to the terminal 137of the source of alternating current while an opposite terminal of thefixed phase winding 397 and a terminal of the control winding 391 areconnected to a grounded conductor 400.

Servomotor 395 drives through an output shaft 401, gear train 403 andshaft 405 a suitable drive means 407 connected to the potentiometer arm331 of the position follow up potentiometer 335 and a pinion 409, asshown in FIG. 38, to angularly position the red disc 57 having providedtherein a spiral slot, as heretofore described.

A portion of the spiral slot in disc 57, which corresponds to the offsetdistance voltage selected by the operator adjustment of the knob 300,coincides with the radial slot provided in the fixed red disc 55 so asto permit a beam of light passing through the blue discs 60 and 58 to inturn pass through a small clear opening formed by the intersections ofthe slots of the discs 57 and 55 and which beam of light will thenappear to the observer at the front of the display instrument to be ablue dot 77 of light on the grid 32 having a geometric shape defined bythe edges of the radial slot in the red disc 55 and the spiral slot inthe red disc 57. The remaining blue light passing through the redcolored disc 55 and 57 will be filtered until it is dim in comparison tothe blue dot 77 of light indicative of the waypoint.

Upon the red disc 57, provided with the spiral slot, being in an angularposition other than that called for by the offset distance voltage ofthe potentiometer 309, the opposing voltage provided by the positionfollow-up potentiometer 335 will not balance that of the offset distancevoltage and an electrical distance error voltage will be induced in thesecondary winding 375 of the coupling transformer 327. The induced errorvoltage will in turn be amplified by the servo amplifier 383 to causethe servomotor 395 to be driven in a sense to angularly reposition thedisc 57 through the gear train 403, together with the potentiometer arm331 of the position follow-up potentiometer 335 until the angularposition of the red disc 57 corresponds to the ofiset distance.Thereupon the angular position of the potentiometer arm 331 in relationto the variable resistor 333 of the position follow-up potentiometer 335will be such that the opposing output voltage provided by thepotentiometer 335 will balance the distance voltage provided by theoffset distance setting potentiometer 309. Such opposing voltagesapplied in the primary winding 325 of the coupling transformer 327 willthen be in a balanced relation so as to induce a null error signalvoltage in the secondary winding 375 of the transformer 327. whereuponthe operation of the servomotor 395 will terminate and the red disc 57will be in such an angular position that the spiral slot providedtherein will be in a proper position relative to the radial slot in thedisc 55 as to effectively project a blue dot 77 of light upon the grid32 in a position indicative of the waypoint, as shown graphically byFIG. 6.

VEHICLE POSITION (RED DOT 75) In projecting the vehicle positionindicator red dot 75 onto the grid 32 as shown in FIG. 1, the blue disc58 in which is provided a radial slot is angularly adjusted to aposition corresponding to the actual vertical plane angle of theaircraft in flight to the aimpoint, indicated in FIG. 1 by the centerpoint 35 of the grid 32. Based on the geometric comparison previouslydescribed and shown graphically in FIGS. 4, 5 and 6, the navigationcomputer 110 of FIG. 3C is so arranged as to apply across outputterminal 420 and the grounded output terminal 145 an alternating currentsignal voltage of a frequency corresponding to that of the frequency ofthe source of alternating current 135 and of a phase corresponding tothat of the phase of the alternating current applied across the outputterminals 137 and 139 or terminals 139 and 141 of the source 135dependent upon whether the actual angle to the aimpoint of the aircraftin flight is ascending, as shown graphically in FIG. 5, or descending asshown graphically in FIGS. 4 and 6.

This signal voltage which is of a magnitude proportional to the actualvertical plane angle of the aircraft in flight to the aimpoint.Furthermore the actual angle to aimpoint signal voltage applied acrossthe terminals 145 and 420 is compared to an opposing slider voltageprovided by a position followup potentiometer 425.

Thus the terminal 420 is connected by an electrical conductor 427 to oneterminal of a primary winding 429 of an output coupling transformer 431and which primary winding 429 has an opposite terminal connected by aconductor 433 to the variably positioned arm 435 operatively positionedin relation to a variable resistor 437 of the position follow-uppotentiometer 425. The resistor element 437 has a grounded center tap439 and one terminal of the resistor 437 is connected by an electricalconductor 441 to switch contacts 443 and 445 controlled by relay switcharms 447 and 449 respectively of a reversing relay 450.

The relay switch 447 is normally biased under spring tension so as toopen the switch contact 443 and close a switch contact 452 connected bya conductor 454 to an opposite end of the resistor element 437 from thatof the conductor 441. Further the relay switch arm 449 is normallybiased under spring tension into a contacting relation with the contact445 and into a position opening a switch contact 456. The switch contact456 is connected by an electrical conductor 458 to the conductor 454leading to the opposite end of the resistor 437 from the conductor 441.

The reversing relay 450 includes an electromagnetic control winding 460effective upon energization to bias the relay switch arm 447 out of aswitch closing relation with the contact 452 and into a position toclose the switch contact 443, while the relay switch arm 449 will besimultaneously biased out of switch closing relation with the contact445 and into a position to close the relay switch contact 456.

In this connection, it may be noted that the relay switch arm 447 isconnected by an electrical conductor 462 which leads, as shown by FIG.3A, through the conductors 162 and 164 to the terminal 141 of the sourceof alternating current 135. The relay switch arm 449 is connected by anelectrical conductor 465, which leads as shown by FIG. 3A, through theconductors 217, 161 and 163 to the terminal 137 of the source ofalternating current 135. The alternating current thus applied throughthe conductor 462 to the relay switch arm 447 will be of a phase whichleads by 180 the phase of the alternating current applied through theconductor 465 to the relay switch arm 449. It will be seen then that solong as the reversing relay 450 is deenergized the alternating currentapplied through the relay switch arm 447 and conductor 454 to one end ofthe resistor element 437 will lead by 180 the phase of the alternatingcurrent applied through the relay switch arm 449 and conductor 441 tothe opposite end of the resistor element 437. However upon theelectromagnetic relay 450 being energized, as hereinafter explained, therelay switch arms 447 and 449 will be actuated so as to open therespective switch contacts 447 and 445 and close the switch contacts 443and 456 respectively so as to reverse the alternating currentsheretofore applied at the respective opposite ends of the resistorelement 437 of the potentiometer 425 for a purpose which will beexplained in greater detail hereinafter.

The actual angle to aimpoint signal voltage applied by the computer tothe conductor 427 is compared in the primary winding 429 of the signalcoupling transformer 431 to a slider signal voltage applied by thepotentiometer 425 to the potentiometer arm 435 and thereby to theconductor 433 connected to the primary winding 429 so as to effect adifference voltage in the primary winding 429 which induces an errorsignal voltage in the secondary winding 475 of the output couplingtransformer 431.

One terminal of the secondary winding 475 is connected to a groundedconductor 477 while the opposite terminal of the secondary winding 475is connected by an electrical conductor 479 to an input terminal 481 ofa servo amplifier 483 having a grounded input-output terminal 485. Anopposite output terminal 487 of the servo amplifier 483 is connected byan output conductor 489 to one terminal of a control winding 491 of atwo phase servomotor 493. The opposite terminal of the control winding491 is connected to a grounded conductor 495. The servomotor 493 alsoincludes a fixed phase winding 497 connected at one terminal to thegrounded conductor 495 and at an opposite terminal through a conductor499 to the conductor 465 leading in turn through conductors 217, 161 and163 to the terminal 137 of the source of alternating current 135.

Servomotor 493 drives through an output shaft 501, gear train 503, shaft505, and shaft 507 a pinion 509 for angularly positioning the blue disc58 having provided therein a radial slot, as heretofore explained. Theshaft 507, as thus driven by the servomotor 493, is also drivinglyconnected through a gear train 511, shaft 513 and shaft 515 so as toangularly position the slider arm 435 of the potentiometer 425 inresponse to the error signal applied through the output couplingtransformer 431 to position the potentiometer arm 435 in a sense to nullthe error signal.

In the aforenoted operation, it should be noted that the potentiometer425 produces a voltage proportional to the angle between the radial slotprovided in the blue disc 58 and the horizontal center line 28 of thegrid 32, as shown by F l6. 1.

During such operation in the event the voltage from the potentiometer425 does not agree with the actual angle signal voltage provided at theconductor 427 by the computer 1 10, then the output signal transformer431 transmits a difference or error voltage to the servo amplifier 483which in turn signals the servomotor 493 to drive through the gear train503 so as to reposition the blue disc 58, having the radial slottherein, in an angular sense to bring the radial slot intocorrespondence with the actual vertical plane angle of the aircraft inflight to the aimpoint as signalled by the computer 110 and at whichadjusted angular position of the blue disc 58 the slider arm 435 of thepotentiometer 425 will be so positioned by the servomotor 493 throughthe gear train 511 and shafts 513 and 515 as to provide an output signalvoltage from the potentiometer 425 which balances that of the signalvoltage applied by the computer 1 10 at the conductor 427. This will inturn null the controlling error signal voltage whereupon the servomotor493 will have angularly positioned radial slot provided in the blue disc58 to a position corresponding to that called for by the actual angle toaimpoint signal voltage provided by the computer 110.

It should be further borne in mind, however, that the vehicle oraircraft in actual flight may be preceeding either (1 towards or (2)away from the space position (aimpoint) indicated in the display of FIG.1 by the center point 35. In the first situation l) the position of theaircraft will be indicated at the left of the vertical line 26, as shownby FIG. 1 by the red dot 75; or in the second situation (2) upon thevehicle or aircraft travelling away from the space position (aimpoint),the position of the aircraft on the grid 32 would be indicated by a reddot 75 at the right of the vertical line 26.

In the present invention, there is provided means to assure a correctdisplay of the aircraft red dot 75 on either side of the grid verticalcenter line 26 dependent upon the flight position thereof in relation tothe aimpoint or center point 35. This is effected through the operationof the reversing relay 450, shown diagrammatically in FIG. 3C, asexplained hereinafter.

The reversing relay 450 in providing means to assure this desireddisplay operation includes a relay control winding 460 which uponenergization and deenergization causes actuation of the relay switcharms 447 and 449 to reverse the connections of the leading and laggingphase terminals 141 and 137 respectively of the source of alternatingcurrent 135 across the position follow up resistor 425, as heretoforeexplained, and in addition energization and deenergization of the relaywinding 460 also causes actuation of a relay switch arm 518 toselectively open and close relay switch contacts 520 and 522. The relayswitch arm 518 is normally biased under spring tension to close theswitch contact 520 while relay switch arm 518 upon energization of therelay winding 460 is actuated to a position opening the switch contact520 and closing the relay switch contact 522. The switch arm 518 isconnected by an electrical conductor 524 to the conductor 479 while therelay switch contact 520 is connected by an electrical conductor 526 toan angularly positioned switch arm 528 of an ambiguity switch 530 andthe relay switch contact 522 is connected by an electrical conductor 532to an angularly positioned switch arm 534 of an ambiguity switch 536.The switch arm 528 of the ambiguity switch 530 and the switch arm 534 ofthe ambiguity switch 536 are driven from a common shaft 540 operablyconnected to the shaft 507 driven through a gearing 503 and shaft 501 bythe servomotor 493. The switch arm 528 is arranged to selectively makeelectrical contact with an arcuate contact element 542 having an opencontact range 545 effective during normal operation in which theangularly positioned switch arm 528 is out of electrical contactingrelation with the arcuate switch contact element 542.

Similarly in the ambiguity switch 536 the angularly positioned switcharm 534 is arranged to selectively make electrical contact with anarcuate switch contact element 552 having an open contact range 556effective during normal operation in which the switch arm 534 is out ofcontacting relation with the arcuate switch contact element 552.

The normal operating range of the ambiguity switch 530 extends over anopen contact range 545 of approximately 180 and from about 180 to 360while the normal operating open contact range of the ambiguity switch536 extends over alike 180 range 556 of from about to 180 arranged in adiametrically opposite relation to that of the open contact range 545,as best shown diagrammatically in FIG. 3B. Both of the arcuate contactelements 542 and 552 are connected by an electrical conductor 550connected at 555 to the electrical conductor 465 leading, as heretoforeexplained, from the terminal 137 of the source of alternating currentI35.

The angularly positioned switch arms 528 and 534 are arranged in a likeangular relation on the common drive shaft 540 so that upon one of theswitch arms 528 or 534 being positioned in the normal open contactoperating range of 545 or 556, respectively, the other of the saidswitch arms will be in a contacting relation with the arcuate switchelement 542 or 552 as the case may be. It will be seen then that whetherthe one or the other of the switch arms in electrical contact with thearcuate switch element 542 or 552 will be operatively effective will bedependent upon whether the one or the other ambiguity switch 530 or 536is rendered effective by the relay switch 518 closing the switch contact520 or 522 of the reversing switch 450 controlling the effectiveoperation thereof In the example shown in FIG. 38 with the reversingrelay 450 being deenergized, it will be seen that the relay switch arm5l8 will close contact 520 and inasmuch as the switch arm 528 of theambiguity switch 530 is shown positioned in the open contact range 545or normal operating range shown diagrammatically in the example 38,there will be no action effected by the ambiguity switch 530.

However upon the reversing relay 450 being energized, the relay winding460 would thereupon cause the relay switch arm 518 to be biased out ofcontacting relation with the switch contact 520 and into a closingcontact relation with the switch contact 522. It will be seen then thatin the example illustrated by FIG. 3B, the ambiguity switch 536 wouldthen be brought into operation, in that the switch arm 534 in makingelectrical contact with the arcuate switch contact element 552 wouldthereupon electrically connect the alternating current applied acrossthe terminals 137 and 139 of the alternating current source directlyacross the input lines 479 and 485 to the servo amplifier 483. Suchconnection would cause the servomotor 493 to be driven in a sense toangularly position the contact arm 534 out of the contacting relationwith the switch element 552 and into the open contact normal operatingrange 556. Such operation would also cause the shaft 507 driven by theservomotor 493 to also effect an angular adj ustment of the blue disc 58so that the radial slot therein would be adjusted angularly from aposition to the left of the center point 35 of the display of FIG. 1 toa position to the right of the center point 35. Thereafter the normalcontrol operation of the servomotor control system in response to theactual angle to aimpoint signal voltage applied by the computer l 10would become effective.

Similarly upon the reversing relay 450 becoming deenergized, the relayswitch arm 518 under spring tension would thereupon open the switchcontact 522 and close the relay switch contact 520. Such action, as uponinitiation of operation of the display, would bring into effect theambiguity switch 530 which would then have the angularly positionedswitch arm 528 in a contacting closing relation with the arcuate switchcontact element 542 and thereupon once again connect across the inputlines 479 and 485 of the amplifier 483 the alternating current outputapplied across the terminals 137 and 139 of the source of alternatingcurrent 135. This would again cause the servomotor 493 to drive throughthe shafts 507 and 540 the switch arm 528 out of contacting relationwith the arcuate switch contact element 542. Simultaneously the switchcontact element 534 would again move into contacting relation with thearcuate switch element 552 of the ambiguity switch 536. This actionwould in turn also cause the blue disc 58 to be driven by the shaft 507in a sense to position the radial slot therein once again to the left ofthe center point 35 of the display of FIG. 1. Thereafter normal controloperation of the servo system by the servomotor 493 would be broughtinto operation so that the red dot 75 indicative of the position of theaircraft would once again be shown to the left of the vertical line 26in accordance with the actual angle to aimpoint signal voltage appliedby the navigation computer I 10 to the output line 427, as heretoforeexplained.

It will be seen from the foregoing that since the vehicle or aircraft inactual flight may be proceeding towards the space position (aimpoint)indicated in the display of FIG. 1 by the numeral 35 in which case theaircraft position should be shown at the left of the vertical line 26 bythe red dot 75, as shown in the example of FIG. 1. Moreover the aircraftmay be travelling away from the space position or center point 35 inwhich case the red dot aircraft indicated position 75 should be shown atthe right of the vertical line 26 of FIG. 1.

It is necessary then to provide the ambiguity switch means 530 and 536and to control of the reversing relay 450 so as to effect the display ofthe aircraft red dot 75 from one side or the other of the grid verticalcenter line 26. Moreover in order to control the energization of thereversing relay 450, there may be provided in the navigation computer110 a device to produce the horizontal location of the space position ofthe aircraft as for example by a conventional Vortac" device,course-line computer, or inertial platform to effect in the navigationcomputer 110 and across output terminal 575 and grounded output terminal145 a from signal voltage applied through a line 577 to the relaywinding 460 and in turn through a grounded conductor 579 serves toeffect energization of the relay 450, as upon the aircraft travellingaway from the space position or aimpoint indicated by the center point35 of the display of FIG. 1.

Thus upon the from signal being applied at the output terminal 575 ofthe computer 110 the relay 450 is rendered effective to connect theambiguity switch 536 into operative relation with the servo amplifier483 and thereby cause servomotor 493 to angularly position the blue disc58 and the radial slot provided therein to a position at the right sideof the center point 35 of the instrument phase of display device asshown in FIG. 1.

Moreover the ratio of the gear train 51 1 is so computed that the switcharm 435 of the potentiometer 425 driven by the servomotor 493 throughthe gear train 511 will thereupon be so positioned as to produce anoutput voltage from the potentiometer 425 proportional to the anglebetween the blue disc radial slot and the right horizontal center line28 of the grid 32.

Furthermore, since it is recognized that the actual angle signal voltageapplied at the output terminal 420 of the navigation computer 110 doesnot change its positive or negative sense, the relay 450 is so arrangedthat upon energization the control winding 460 of the relay 450 actuatesthe other relay switch arms 447 and 449 so as to close the relay switchcontacts 443 and 456, respectively, so as to in effect reverse theexcitation to the potentiometer 425 from the source of alternatingcurrent 135 so that the controlling error signal voltage induced in thesecondary winding 475 and applied through the servo amplifier 483 to thecontrol winding 491 of the servomotor 493 will be of a proper phasesense to cause the servomotor 493 to drive the blue disc 58 in a propersense and direction to effect the display of the aircraft indicator reddot 75 properly at the right of the vertical line 26.

However cessation of the from" signal causes the operation of the relay450 to disconnect the ambiguity switch 536 and connect into operationthe alternate ambiguity switch 530 so as to effect through the servoamplifier 483 the positioning of the radial slot of the blue disc 58 bythe servomotor 493 to the left side of the vertical line 26 of theinstrument face of the display instrument, as shown in FIG 1.

The control arm 435 of the potentiometer 425 will be thereupon driventhrough the gear train 511 by the servomotor 493 in such a manner thatthe potentiometer in the normal operating range 545 of the ambiguityswitch 542 produces a voltage proportional to the angle between theradial slot of the blue disc 58 and the left horizontal center line 28of the grid 32 of the display device of FIG. 1.

In the foregoing operation of the blue disc 58, it should be borne inmind that the spiral slot of the blue disc 60 is so angularly positionedin relation to the angular position of the radial slot of the blue disc58 that the position of the aircraft indicator red light dot 75projected onto the grid 32 corresponds to the vertical plane slantdistance to the aimpoint or center point 35.

In effecting such operation, the navigation computer 110 provides at anoutput terminal 600 by conventional means, a voltage proportional to thealtitude difference between the aircraft in flight and the preselectedaltitude, as indicated graphically at FIGS. 4, and 6. The computer 110output altitude difference signal voltage is applied through a conductor602 to an input terminal 604 of an amplifier 606 having a groundedinput-output terminal 60S.

The amplifier 606 includes a sine function potentiometer 610 having avariable resistor element 612 and an adjustable resistor arm 614adjustably positioned in relation to the resistor element 612 by a shaft616 drivingly connected to the output shaft 513 of the gear train 511driven by the servomotor 493 in response to the actual angle to aimpointsignal voltage applied at the terminal 420 of the navigation computer110.

The resistor element 612 and variable resistance adjustment arm 614 areconnected by electrical conductors 618 and 620 respectively inconventional manner into the amplifier circuitry of the amplifier 606 soas to adjust the gain of the amplifier 606 dependent upon the actualangle to aimpoint signal voltage and in such a manner that the outputvoltage of the amplifier 606 applied at the output terminal 625 is aproduct of the altitude difference voltage applied at the outputterminal 600 of the computer and the reciprocal of the actual angle sinefunction, and which product provides an output signal voltage indicativeof the slant distance from the vehicle in flightto the selectedaimpoint, as shown graphically by FIGS. 4, 5 and 6.

This slant distance voltage applied across the output terminals 625 and608 of the amplifier 606 is in turn applied through a conductor 627 to aterminal of a primary winding 629 of an output signal transformer 631.An opposite terminal of the primary winding 629 is connected by aconductor 633 to an adjustable arm 635 of a variable position follow-uppotentiometer 637 having a resistor element 639 variably contacted bythe resistor arm 635. One terminal of the resistor element 639 isconnected to a grounded input-output conductor 641 while the oppositeterminal of the resistor element 639 is connected through a conductor643 to an electrical conductor 339 which as shown by FIG. 3A leads tothe variable range slant distance excitation voltage provided at thesource of alternating current 135, as hereinafter explained in greaterdetail.

This slant distance excitation voltage applied across the resistor 639of the potentiometer 637 provides an output voltage from thepotentiometer 637 which is applied to the primary winding 629 inopposition to the slant distance to a aimpoint signal voltage appliedthereto through the conductor 627.

The slant distance to aimpoint signal voltage applied to the conductor627 is thus compared in the primary winding 629 to the output of thepotentiometer 637 and the resultant difference voltage induces in asecondary winding 650 an error signal voltage. The secondary winding 650has one terminal connected to a grounded conductor 652 while theopposite terminal of the secondary winding 650 is connected by aconductor 654 to an input terminal 656 of a servo amplifier 658 having agrounded input-output terminal 660 and an opposite output terminal 662from which leads an output conductor 664 to a terminal of a controlwinding 666 of a two phase servomotor 668. The opposite terminal of thecontrol winding 666 is connected to a grounded conductor 670. Theservomotor 668 has a fixed phase winding 672 having one terminalconnected to the grounded conductor 670 and an opposite terminalconnected by a conductor 675 to the conductor 465 leading in turn, asshown in FIG. 3A, to the output terminal 137 of the source ofalternating current 135.

Servomotor 668 drives through an output shaft 680, a gear train 682, andshafts 685 and 687 to adjustably position the ann 635 of thepotentiometer 637. Also the output shaft 687, as shown by FIG. 3B, isconnected to an input element of a mechanical differential mechanism 690having a second input element driven by a shaft 692 leading from theshaft 507 driven by the servomotor 493. The mechanical differentialmechanism 690 has an output shaft 694 which in turn is operablyconnected to a pinion 696 for angularly positioning the blue disc 60having the spiral slot, as heretofore specified.

It will be seen from the foregoing arrangement that the slant distanceto aimpoint signal voltage applied at the conductor 627 is compared tothe output of the potentiometer 637 having the variable control arm 635driven by the servomotor 668 through a suitable gearing together withthe blue disc 60 to angularly position the spiral slot therein. Upon theposition of the slant distance potentiometer control arm 635 being outof agreement with the slant range voltage applied at the conductor 627an error signal voltage will be induced by the primary winding 629 ofthe coupling transformer 631 into the secondary winding 650 and whichinduced error signal voltage is in turn applied to the input of theservo amplifier 658 so as to cause the control winding 666 of theservomotor 668 to cause the servomotor 668 to reposition the control arm635 of the potentiometer 637 together with the blue disc 60 in a senseto null the error signal voltage induced in the secondary winding 650.

In the aforenoted arrangement, the gear train 682 driven by theservomotor 668 has the output shaft 685 thereof connected to the shaft687 to adjustably position the arm 635 of the potentiometer 637 as wellas effect through the mechanical differential mechanism 690 rotation ofthe pinion 696 to angularly position the blue disc 60.

it should be further noted that the mechanical differential mechanism690 has the second input shaft 692 connected through the shaft 507 tothe shaft 505 and thereby to the output of the actual angle to aimpointcontrolled servo gear train 503. Thus when the actual angle to theaimpoint voltage applied by the computer 110 to the conductor 427changes, causing in turn the servomotor 493 to efiect a change in theangular position of the blue disc 58 and the radial slot providedtherein, the mechanical differential mechanism 690 also causes theangular relationship of the blue disc 60 having a spiral slot therein tobe varied in relation to the radial slot of the blue disc 60. Thereupon,the relationship of the spiral slot in the blue disc 60 to the radialslot of the blue disc 58 will be such as to permit passage of the beamof red light through the coinciding openings of the two slots to producethe red dot 75 on the grid 32 at a position indicative of the properslant distance for the new angular position of the blue disc 58 bearingthe radial slot.

Instrument Scaling The distance, altitude and angular scales of thedisplay instrument are selected to suit the speed, altitude andmaneuvering capability of the vehicle or aircraft in which it is to beused. The scales would be quite different for a helicopter than for asupersonic transport for example, although the display method and meansmay be substantially the same for either. Furthermore, in the presentinvention means are provided to change the indicator scalesautomatically upon the aircraft or vehicle in flight coming within therange of the larger (more sensitive) scales.

Referring to the drawings of FIG. 3A, it will be seen that thealternating current power supply 135 through the operation of slantdistance excitation control relays 345 and 355 selectively applies tothe output conductor 339 a slant distance alternating current excitationvoltage which may be in the different excitation ranges provided by thesource of alternating current 135, including a relatively low range asprovided at the terminal 361 or in a relatively medium range as providedat the terminal 363 or in a relatively high range as provided at theterminal 365 of the source of alternating current 135. The slantdistance alternating current excitation voltage thus applied at theconductor 339 is applied across both the resistor 333 of the offsetdistance potentiometer 335 and the resistor 639 of the slant distancepotentiometer 637 so as to thereby set the presentation scale factor ofthe display instrument, as hereinafter explained in greater detail.

The slant distance excitation control relay 345 has an electromagneticcontrol winding 704 while the slant distance excitation control relay355 has an electromagnetic control winding 706. The control winding 704of the relay 345 upon energization is effective to magnetically bias therelay switch element 341 out of a contacting relation with the relaycontact 347 and into a contacting relation with a relay contact 710. Therelay contact 710 is connected by an electrical conductor 712 to theterminal 365 of the source of alternating current 135 and is thereuponeffective upon the relay switch arm 341 closing the contact 710 toconnect the output conductor 339 to the relatively high range ofalternating current applied at the terminal 365.

The control winding 704 upon energization is also effective to biassimultaneously a relay switch arm 714 out of contacting relation with arelay contact 715 and into contacting relation with a relay contact 716and a relay switch arm 718 into contacting relation with a relay switchcontact 720. The relay switch arm 714 is normally biased under springtension into contacting relation with the relay contact 715 and out ofcontacting relation with the contact 716 while the relay switch arm 718is normally biased out of contacting relation with the contact 720.

The relay switch arm 714 is connected by an electrical conductor 722 toone terminal of the source of electrical energy or battery 725 having anopposite terminal connected by a conductor 726 to ground. The relaycontact 716 is connected by an electrical conductor 728 to terminals ofelectrically illuminated annunciator lights 37 and 39 having oppositeterminals connected to grounded conductors 730 and 732 as shown in FIG.3A.

Thus upon the control winding 704 being energized to electromagneticallyactuate the relay switch arm 714 into the contacting relation with therelay contact 716, the source of electrical energy 725 is connectedacross the annunciator lights 37 and 39 to eifectively illuminate thesame so as to indicate to the operator that the display instrument hasbeen rendered effective for operation in a 200 mile and 100,000 footscale range by the connection of the relatively high range alternatingcurrent terminal 365 of the source of alternating current 135 to thedistance potentiometers 335 and 637.

The excitation of the control relay winding 704 of the slant distanceexcitation control relay 345 is also effective to actuate a relay switcharm 718 into contacting relation with a switch contact 720 to rendereffective a range change trigger switch 735 for controlling theoperation of an OR" gate 737 which in turn controls the energization ofthe winding 704 of the relay 345.

In etfecting the latter operation, it will be noted that the relayswitch contact 720 is connected by an electrical conductor 733 to acontrol terminal 734 of the OR" gate 737 The relay switch arm 718 isnormally biased under spring tension to an open contacting relation withthe relay switch contact 720. However upon energization of the relaycontrol winding 704 the switch arm 718 is actuated into contactingrelation with the relay contact 720. The relay switch arm 718 hasconnected thereto a conductor 740 which, as shown in F [(37 3D, isconnected to an arcuate segmental switch element 742 which may becontacted over a range of movement of approximately 270 by an arcuatelymovable switch arm 745, while over a second range of arcuate movement ofapproximately indicated by the numeral 747, the switch arm 745 iseffectively out of contacting relation with the arcuate segmental switchelement 742.

The switch arm 745 of the range change trigger switch 735 is connectedto an electrical conductor 750 which is in turn connected at 555 to theconductor 465 leading as heretofore explained through the conductors217, 161 and 163 to the terminal 137 of the source of alternatingcurrent 135, as shown in FIG. 3A. The arm 745, as shown in FIG. 3B ismechanically driven through a shaft 752 operably connected to the outputshaft 687 leading through the mechanical differential mechanism 690 andshaft 694 to the pinion 696 drivingly connected to the blue disc 60provided with the spiral slot.

The arrangement of the range change trigger switch 735 is such that theswitch arm 745 thereof will be in effective contacting relation with thearcuate switch element 742 so long as the blue disc 60 is angularlypositioned over the normal operating range of the spiral slot therein aseffected by the operation of the differential mechanism 690 by the shaft687 which is also drivingly connected through the shaft 752 to the arm745. However upon the angular adjustment of the blue disc 60 so that thespiral slot therein is positioned out of its normal operating range andinto the range of the larger (more sensitive) scales, the arms 745 ofthe range change trigger switch 735 will be adjusted out of contactingrelation with the arcuate switch element 745 and into the open contactrange 747. Thereupon the alternating current applied through theconductor 740, relay switch arm 718, contact 720 and conductor 733 tothe control terminal 734 of the OR gate 737 would be effectively removedby the switch arm 745 moving out of contacting relation with the arcuatesegmental switch element 742 so as to permit the OR" gate 737 to removethe voltage signal applied to the output terminal 753 connected througha conductor 755 to the control winding 704 of the relay 345.

However also controlling the electrical input applied across the outputterminal 753 and the grounded input-output terminal 754 of the OR gate737 are other control terminals 760 and 762 of the OR" gate 737.

The control terminal 760 is connected through an electrical conductor765 to a high signal voltage output terminal 767 of a voltage leveldetector 769 having a grounded input-output terminal 771 and an oppositeinput terminal 773 connected through an electrical conductor 775 to theconductor 323 at 777 so that the voltage level detector 769 senses theoffset distance voltage applied at the output of the potentiometer 309.

Upon the selected offset distance voltage exceeding a predetermined highlevel the voltage level detector 769 is effective to apply across theoutput terminals 767 and 771 a high voltage signal which is appliedthrough the conductor 765 to the control terminal 760 of the OR gate 737so as to maintain across the output terminals 753 and 754 of the OR gate737 an output signal voltage applied through the output conductor 755 tomaintain the control winding 704 of the slant distance excitationcontrol relay 345 in an energized condition.

Further the remaining control terminal 762 of the OR gate 737 isconnected by an electrical conductor 780 to a high voltage signal outputterminal 783 of a voltage level detector 785 having an input-outputterminal connected to a grounded conductor 787 and an opposite inputterminal 789 connected by a conductor 790 to the slant distance towaypoint signal voltage conductor 627 at a point 792 so that the voltagelevel detector 785 is effective to sense the slant distance to waypointsignal voltage applied across the output terminals 625 and 608 of theamplifier 606.

The arrangement of the voltage level detector 785 is such that when theslant distance to waypoint signal voltage at the line 627 exceeds apredetermined high level the detector 785 is effective to apply a signalhigh" voltage to the control terminal 762 of the OR gate 737 so as torender the OR" gate 737 effective to maintain an energizing currentthrough the control winding 704 of the slant distance excitation controlrelay 345. The OR gate 737 is of a conventional type arranged to providethe energizing voltage through the output conductor 755 to the controlwinding 704 of the relay 345 upon any one or more of the controlterminals 734, 760 and 762 having applied thereto a control signalvoltage. The OR gate 737 is effective to terminate the energization ofthe control winding 704 of the relay 345 only upon a control signalvoltage being applied to none of the control terminals 734, 760, and762.

However upon the control winding 704 of the relay 345 becomingdeenergized the respective relay switch arms 341, 714 and 718 returnunder spring tension to the position shown in FIG. 3A in which theswitch arm 714 and 718 open the respective relay contacts 716 and 720and the relay switch am 341 opens the relay contact 710 and closes therelay contact 347 connected through the conductor 349 to the switch arm351 of the companion control relay 355.

Upon deenergization of the control winding 706 of the slant distanceexcitation control relay 355, the relay switch arm 351 is biased underspring tension into contacting relation with a relay contact 357connected through a conductor 359 to the relatively low rangealternating current output terminal 361 of the source of alternatingcurrent 135. Thus upon deenergization of both the control relay winding704 of the relay 345 and the control relay winding 706 of the relay 355the relay switch arms 341 and 351 are thereupon rendered effective toconnect the output conductor 339 to the relatively low range ofalternating current applied at the terminal 361 of the source ofalternating current 135.

The control winding 706 of the relay 355 upon energization is effectiveto magnetically bias the relay switch element 351 out of a contactingrelation with the relay contact 357 into a contacting relation with arelay contact 800. The relay contact 800 is connected by an electricalconductor 802 to the relatively medium range alternating current outputterminal 363 of the source of alternating current and is thereuponeffective upon the relay switch arm 341 of the companion control relay345 closing the contact 347 to connect the output conductor 339 throughthe switch arm 341, relay contact 347, conductor 349, switch arm 351,relay contact 800 and conductor 802 to the relatively medium range ofalternating current applied at the terminal 363 of the source ofalternating current 135 The control winding 706 upon energization isalso effective to bias simultaneously a relay switch arm 805 intocontacting relation with a relay contact 806 and a relay switch arm 808into contacting relation with a relay switch contact 810. The relayswitch arms 805 and 808 are normally biased under spring tension out ofcontacting relation with the respective relay contacts 806 and 810.

The relay switch arm 805 is connected by an electrical conductor 812 tothe relay contact 715 of the companion control relay 345 so that upondeenergization of the control winding 704 of the relay 345 the switcharm 805 is connected through the electrical conductor 812, switchcontact 715 and relay switch arm 714 to the source of electrical energyor battery 725.

Relay switch contact 806 is connected by an electrical conductor 814 toelectric terminals of electrical illuminated annunciator lights 35 and41 having opposite terminals connected to grounded conductors 818 and820, as shown in FIG. 3A. Thus, upon the control winding 704 of therelay 345 being deenergized and the control winding 706 of the relay 355being energized, the relay switch arm 714 will be biased under springtension into a position closing the relay contact 715 and the relayswitch arm 805 will be actuated by the energized electromagnetic controlwinding 706 into a position closing the switch contact 806. The sourceof electrical energy 725 will be then connected across the annunciatorlights 35 and 41 so as to effectively illuminate the same and indicateto the operator that the display instrument has been rendered effectivefor operation in a 20 mile and 10,000 foot scale range by the connectionof the relatively medium alternating current terminal 363 of the sourceof alternating current 135 to the distance potentiometers 335 and 637.

The energization of the control winding 706 of the shunt distanceexcitation control relay 355 is also effective to actuate a relay switcharm 808 into contacting relation with a switch contact 810 so as torender effective the range change trigger switch 735 for controlling theoperation of an OR gate 837 having an output terminal 853 and a groundedinputoutput terminal 854. The OR gate 837 in turn controls theenergization of the control winding 706 of the relay 355.

In effecting the latter operation, it will be noted that the relayswitch contact 810 is connected by an electrical conductor 833 to acontrol terminal 834 of the OR gate 837. Relay switch arm 808 isnormally biased under spring tension to an open contacting relation withthe relay switch contact 810. However upon energization of the controlwinding 706 the switch arm 818 is actuated into contacting relation withthe relay contact 810. The relay switch arm 808 has connected thereto anelectrical conductor 840 which as shown in FIG. 3A is connected at 842to the conductor 740 leading to the arcuate switch element 742 of therange change trigger switch 735.

The range change trigger switch 735 is arranged to apply through therelay switch arm 808 and closed relay switch contact 810 a signalvoltage through the conductor 833 to the control terminal 834 of the ORgate 837 to render the 012" gate 837 effective to apply across outputterminals 853 and 854 an energizing voltage. The energia'ng voltage isapplied through an output conductor 855 leading from the output terminal853 of the OR gate 837 to a terminal of the control winding 706 of therelay 355 having an opposite terminal connected to a grounded conductor857 to effect the energization of the control winding 706.

Thus so long as the blue disc 60 is angularly positioned within thenormal operating range of the spiral slot therein, the switch element745 makes electrical contact with the arcuate switch element 742 of therange change trigger switch 735, and a voltage will be applied to theOR" gate 837 so as to assure the application of a signal voltage throughthe output conductor 855 for maintaining the relay winding 706energized.

The OR" gate 837 includes additional control terminals 860 and 862. Aconductor 865 leads from the terminal 860 to a medium signal outputvoltage terminal 867 of the voltage level detector 769. The leveldetector 769 is effective upon the sensed offset distance voltageapplied at the conductor 323 exceeding a predetermined medium level toapply through the conductor 865 a medium voltage signal applied to thecontrol terminal 860 of the OR gate 837 so as to maintain a signalvoltage on the output conductor 855 so as to effectively energize thecontrol winding 706 of the relay 355.

Further the output control terminal 862 of the OR" gate 837 is connectedby an electrical conductor 870 to a medium voltage signal terminal 873of the voltage level detector 785. The voltage level detector 785 iseffective upon the sense slant distance to waypoint signal voltageapplied at conductor 627 exceeding a predetermined medium voltage levelto apply across the output terminals 873 and 787 of the voltage leveldetector 785 a medium voltage level signal voltage on the conductor 870which is in turn applied to the control terminal 862 of the OR gate 837to maintain an output voltage on the conductor 855 to cause the controlwinding 706 of the relay 355 to be effectively energized.

In the normal operation of the aforenoted arrangement when the slantdistance to waypoint signal voltage applied at conductor 627 drops belowa preset high level and the slant distance servomotor 668 moves to aposition representing less than the predetermined lower limit of thehigh slant distance range, the operation will be such that thecontrolling signals applied to the OR gate 737 at control terminals 762and 734 by the voltage level detector 785 and the range change triggerswitch 735, respectively, will no longer be present, whereupon theoutput energizing voltage normally applied through the output conductor755 of the OR gate 737 will terminate and the relay 345 will thereuponmove to the deenergized position, causing a shifting of the control ofthe power supply 135 for the operation of the display instrument to therelay 355 and thereby to the medium alternating current output terminal363, as hereinbefore explained. The display instrument is thenconditioned for operation on the 20 mile and 10,000 foot range so longas the control winding 706 of the companion relay 355 is effectivelyenergized, while the control winding 704 of the relay 345 isdeenergized.

The 012" gate 837 and relay 355 function in alike manner to switch thepower supply 135 for operation on the relatively low alternating currentrange terminal 361 and the display instrument for a 2 mile and 1,000foot range, upon the slant distance signal voltage applied at conductor627 decreasing below the lower limit of a medium voltage level as sensedby the voltage level detector 785.

Both the relays 345 and 355 effectively open the circuit from the rangechange trigger switch 735 when they are deenergized so as to prevent anyreactivation of the relay 34S and 355 before restoration of the signalfrom the voltage level detector 785.

The otfset distance voltage level detector 769 operates in the samemanner as the voltage level detector 785, but instead is dependent uponthe selected offset distance voltage to supply a high signal to the ORgate 737 of medium signal to the OR" gate 837 to block action of eitherrelay 345 or 355 upon the offset distance selected by the operator beinggreater than the range to be engaged.

Thus while the range change trigger switch 735 and the slant distance towaypoint signal voltage level detector 785 provide means effective undernormal operating conditions to change the display instrument scalesautomatically upon the vehicle or aircraft in flight coming within therange of the larger (more sensitive) instrument scales; the offsetdistance voltage level detector 769 cooperates in the control system toblock this automatic change in the event the operator selected offsetdistance would otherwise in effect cause an angular adjustment by theservomotor 395 of FIG. 3A of the spiral slot of the offset distance reddisc 57 of FIG. 3B in such a manner as to project the blue dot 77 ofFIG. 1 off of the grid 32 under such larger scale operating conditions.

Further in the aforenoted operation, the relay 345 and 355 also serve toclose circuits to selectively illuminate the annunciator lights 37 and39 or 35 and 41 so as to show the active range of operation of thedisplay instrument.

Further the range change trigger switch 735 and the ambiguity switches530 and 536 serve to place the instrument servos (and display discs) inthe proper areas of operation in the event they are adjusted out ofthese areas upon power being initially applied to the display instrumentto effect operation thereof.

In addition, the ambiguity switch 530 will cause the blue disc 58 toangularly position the radial slot therein from the left side of thevertically extending center line 26 to the right side of the verticalline 26 of the display instrument, as viewed in FIG. 1 upon the aircraftpassing over the aimpoint indicated by numeral 35 of the displayinstrument of FIG. I and proceeding past such point so as to cause afrom signal to be applied by the computer 1 10 to the output conductor577, as viewed in FIG. 3C.

ALTITUDE HOLD However as shown diagrammatically in FIGS. 3A, 3B and 3C,as the vehicle or aircraft in flight approaches the preselected altitudeshown graphically on FIGS. 4, 5 and 6, the navigation computer 1 10 isarranged to provide for an automatic-altitude capture and hold controlof the aircraft in flight. When the computer is operating in the holdmode, a logic voltage signal is provided which is applied across anoutput terminal 900 and the grounded input-output terminal of thecomputer 1 10.

The output terminal 900 of the computer 110 is connected by a conductor902 to a terminal of a electromagnetic control winding 904 having anopposite terminal connected to a grounded conductor 906. Upon thealtitude capture voltage signal being applied across the outputterminals 900 and 145 of the computer 110, control winding 904 iseffectively energized so as to actuate an armature 908 into the coil 904against the biasing force of a spring 910. An actuator arm 912 ispivoted at 914 and operably connected at 916 to the armature 908 so asto cause the flag 49 to be displayed in the opening 48 of the displayinstrument, as shown in FIG. 1. Upon the altitude capture voltage signalbeing terminated the flag 49 under the biasing force of the spring 910will be biased out of the opening 48 into a return position, as showndiagrammatically by FIG. 3B.

When the computer 1 10 is operating in the hold mode, the availablelogic voltage signal is used to position the flag 49 in the mask window48 of the display instrument 10 to indicate to the operator that thevehicle or aircraft is following a horizontal path in the vertical planecorresponding to the preselected altitude indicated graphically in FIGS.4, 5 and 6.

Normally when the navigation computer 110 is operated through analtitude capture maneuver, it automatically transfers the control of theaircraft to an altitude hold mode of operation and the flag 49 will bemaintained in the position in the window 48 exposed to the view of theoperator.

When the navigation computer 110 senses that the aircraft has deviatedfrom the hold altitude condition by a predetermined amount, the altitudecapture signal voltage applied to the conductor 902 will terminatecausing the electromagnetic winding 904 to be deenergized and the flag49 to be biased by the spring 910 out of the window 48 so as todisappear from the view of the operator and thereby warn the pilot thatthe aircraft is no longer at the pre-selected altitude. The flag 49 thusserves as a visual alerting device to warn the pilot of the aircraftthat the aircraft in flight is approaching or departing from apre-selected altitude.

The altitude capture signal conductor 902 is also connected through aconductor 922 to a terminal of another electromagnetic control winding924 of a relay having an opposite terminal of the control winding 924grounded at 926.

The relay winding 924 is arranged to operatively control a relay switcharm 928 normally biased under spring tension to a contact open relationto a relay contact 930. Upon energization of the control winding 924effected by an altitude capture signal voltage being applied through theconductor 902 from the computer 110, the control winding 924 effects anelec' tromagnetic force which biases the switch arm 928 in opposition tothe spring tension thereof into a contact closing relation with therelay contact 930.

The relay switch arm 928 is connected by an electrical conductor 932 toone terminal of a source of electrical energy or battery 934 while theopposite terminal of the battery 934 is grounded at 936. The relaycontact 930 is connected by an electrical conductor 938 to one terminalof an electrically operated audio alarm 940 of a conventional type whichmay be arranged in a headset of the pilot and having an oppositeterminal grounded at 942. Thus upon the relay switch arm 928 closing therelay contact 930 in response to the altitude capture signal voltageapplied at conductor 902 effecting energization of the relay controlwinding 924, the source of electrical energy 934 will be connected tothe audio alarm 940 and there will be generated an audio signal at thealarm or headset 940 of the pilot which will serve as an audible alertto warn the pilot that the aircraft in flight is approaching ordeparting from the pre-selected altitude shown graphically at FIGS. 4,and 6.

While only one embodiment of the invention has been illustrated anddescribed, various changes in the form and relative arrangements of theparts, which will now appear to those skilled in the art may be madewithout departing from the scope of the invention.

What is claimed is:

1. A display instrument comprising a display plate bearing grid linesand an indicia point, and means to project on the display plate a beamof light to show a symbolic relationship of the vehicle in flight to theindicia point and to the grid lines, the indicia point being indicativeof the aimpoint of the vehicle and the grid lines being indicative ofaltitude and distance of the vehicle relative to the aimpoint, othermeans to project on to the display plate a cursor line, means to adjustsaid other means to angularly position the cursor line projected on tothe display plate by said other means so as to define a desired path ofthe vehicle in a vertical plane of flight to the aimpoint indicated bythe indicia point of the display plate, other indicia borne by thedisplay plate and associated with the grid lines to indicate thedistance and altitude of the vehicle shown in symbolic relationship bythe beam of light to both the aimpoint indicated by the indicia point ofthe display plate and to the desired path of the vehicle in the verticalplane of flight defined by the cursor line, and angular indicia borne bythe display plate and associated in cooperative relation with the cursorline to indicate the desired angle of flight ofthe vehicle shown by thebeam of light in symbolic relationship thereto.

2. A display instrument comprising a display plate bearing grid linesand an indicia point, and means to project on the display plate a beamof light to show a symbolic relationship of the vehicle in flight to theindicia point and to the grid lines, the indicia point being indicativeof the aimpoint of the vehicle and the grid lines being indicative ofaltitude and distance of the vehicle relative to the aimpoint,operator-operative means to preselect altitude of flight of the vehicleat the aimpoint indicated by the indicia point of said display plate,and means operated by the operator-operative means to indicate thepreselected altitude of said indicated aimpoint.

3. The combination defined by claim 2 including other means to projectonto the display plate a second beam of light to show a symbolicrelationship of a waypoint of the vehicle in relation to the aimpointand in relation to the position of the vehicle in flight shownsymbolically by the first mentioned beam of light projected onto thedisplay plate, and other operator-operative means to set the other meansto project the second beam of light onto the display plate so as to showsymbolically the waypoint at a predetermined offset distance from theaimpoint indicated by the indicia point.

4. A display instrument comprising a display plate bearing grid linesand an indicia point, and means to project on the dis play plate a beamof light to show a symbolic relationship of the vehicle in flight to theindicia point and to the grid lines, the indicia point being indicativeof the aimpoint of the vehicle and the grid lines being indicative ofaltitude and distance of the vehicle relative to the aimpoint, means tooperably position the light projecting means so that the beam of lightsymbolic of the relationship of the vehicle in flight may be effectivelyshifted from one side of the indicia point borne by the display plate toan opposite side of the indicia point upon the vehicle in flight passingthe aimpoint of the vehicle indicated by the indicia point.

5. A display instrument comprising a display plate bearing grid linesand an indicia point, and means to project on the display plate a beamof light to show a symbolic relationship of the vehicle in flight to theindicia point and to the grid lines, the indicia point being indicativeof the aimpoint of the vehicle and the grid lines being indicative ofaltitude and distance of the vehicle relative to the aimpoint, means tocompute flight distance of the vehicle to the aimpoint indicated by theindicia point of said display plate, and means responsive upon thecomputed flight distance decreasing below a predetermined value toeffect an amplification of the symbolic rela tionship of the beam oflight to the grid lines indicative of the altitude and distance of thevehicle in relation to said indicated aimpoint.

6. The combination defined by claim 5 including means to operablyposition the light projecting means so that the beam of light symbolicof the relationship of the vehicle in flight may be efiectively shiftedfrom one side of the indicia point borne by the display plate to theopposite side of the indicia point upon the vehicle in flight passingthe aimpoint of the vehicle indicated by the indicia point.

7. A display instrument comprising a display plate bearing an indiciapoint indicative of an aimpoint of a vehicle in flight, means to projecton the display plate a beam of light to show a symbolic relationship ofthe vehicle in flight to the indicia point indicative of the aimpoint ofthe vehicle, means to project onto the display plate a cursor lineextending from the indicia point borne by the display plate at one endof the cursor line, and means to position the cursor line projectingmeans so as to pivot the projected cursor line about the indicia pointat said one end of the cursor line so as to define a desired path of thevehicle in a vertical plane of flight to the aimpoint indicated by theindicia point of the display plate.

8. The combination defined by claim 7 including operatoroperative meansto selectively position the means to project onto the display plate thecursor line so as to define a desired path of the vehicle in a verticalplane of flight to the aimpoint in a predetermined angular relation.

1. A display instrument comprising a display plate bearing grid linesand an indicia point, and means to project on the display plate a beamof light to show a symbolic relationship of the vehicle in flight to theindicia point and to the grid lines, the indicia point being indicativeof the aimpoint of the vehicle and the grid lines being indicative ofaltitude and distance of the vehicle relative to the aimpoint, othermeans to project on to the display plate a cursor line, means to adjustsaid other means to angularly position the cursor line projected on tothe display plate by said other means so as to define a desired path ofthe vehicle in a vertical plane of flight to the aimpoint indicated bythe indicia point of the display plate, other indicia borne by thedisplay plate and associated with the grid lines to indicate thedistance and altitude of the vehicle shown in symbolic relationship bythe beam of light to both the aimpoint indicated by the indicia point ofthe display plate and to the desired path of the vehicle in the verticalplane of flight defined by the cursor line, and angular indicia borne bythe display plate and associated in cooperative relation with the cursorline to indicate the desired angle of flight of the vehicle shown by thebeam of light in symbolic relationship thereto.
 2. A display instrumentcomprising a display plate bearing grid lines and an indicia point, andmeans to project on the display plate a beam of light to show a symbolicrelationship of the vehicle in flight to the indicia point and to thegrid lines, the indicia point being indicative of the aimpoint of thevehicle and the grid lines being indicative of altitude and distance ofthe vehicle relative to the aimpoint, operator-operative means topreselect altitude of flight of the vehicle at the aimpoint indicated bythe indicia point of said display plate, and means operated by theoperator-operative means to indicate the preselected altitude of saidindicated aimpoint.
 3. The combination defined by claim 2 includingother means to project onto the display plate a second beaM of light toshow a symbolic relationship of a waypoint of the vehicle in relation tothe aimpoint and in relation to the position of the vehicle in flightshown symbolically by the first mentioned beam of light projected ontothe display plate, and other operator-operative means to set the othermeans to project the second beam of light onto the display plate so asto show symbolically the waypoint at a predetermined offset distancefrom the aimpoint indicated by the indicia point.
 4. A displayinstrument comprising a display plate bearing grid lines and an indiciapoint, and means to project on the display plate a beam of light to showa symbolic relationship of the vehicle in flight to the indicia pointand to the grid lines, the indicia point being indicative of theaimpoint of the vehicle and the grid lines being indicative of altitudeand distance of the vehicle relative to the aimpoint, means to operablyposition the light projecting means so that the beam of light symbolicof the relationship of the vehicle in flight may be effectively shiftedfrom one side of the indicia point borne by the display plate to anopposite side of the indicia point upon the vehicle in flight passingthe aimpoint of the vehicle indicated by the indicia point.
 5. A displayinstrument comprising a display plate bearing grid lines and an indiciapoint, and means to project on the display plate a beam of light to showa symbolic relationship of the vehicle in flight to the indicia pointand to the grid lines, the indicia point being indicative of theaimpoint of the vehicle and the grid lines being indicative of altitudeand distance of the vehicle relative to the aimpoint, means to computeflight distance of the vehicle to the aimpoint indicated by the indiciapoint of said display plate, and means responsive upon the computedflight distance decreasing below a predetermined value to effect anamplification of the symbolic relationship of the beam of light to thegrid lines indicative of the altitude and distance of the vehicle inrelation to said indicated aimpoint.
 6. The combination defined by claim5 including means to operably position the light projecting means sothat the beam of light symbolic of the relationship of the vehicle inflight may be effectively shifted from one side of the indicia pointborne by the display plate to the opposite side of the indicia pointupon the vehicle in flight passing the aimpoint of the vehicle indicatedby the indicia point.
 7. A display instrument comprising a display platebearing an indicia point indicative of an aimpoint of a vehicle inflight, means to project on the display plate a beam of light to show asymbolic relationship of the vehicle in flight to the indicia pointindicative of the aimpoint of the vehicle, means to project onto thedisplay plate a cursor line extending from the indicia point borne bythe display plate at one end of the cursor line, and means to positionthe cursor line projecting means so as to pivot the projected cursorline about the indicia point at said one end of the cursor line so as todefine a desired path of the vehicle in a vertical plane of flight tothe aimpoint indicated by the indicia point of the display plate.
 8. Thecombination defined by claim 7 including operator-operative means toselectively position the means to project onto the display plate thecursor line so as to define a desired path of the vehicle in a verticalplane of flight to the aimpoint in a predetermined angular relation. 9.A display instrument comprising a display plate bearing an indicia pointindicative of an aimpoint of a vehicle in flight, means to project onthe display plate a beam of light to show a symbolic relationship of thevehicle in flight to the indicia point indicative of the aimpoint of thevehicle, means to project onto the display plate a cursor line so as todefine a desired path of the vehicle in a vertical plane of flight tothe aimpoint indicated by the indicia point of the display plate, othErmeans to project onto the display plate a second beam of light to show asymbolic relationship of a waypoint of the vehicle in relation to theaimpoint and in relation to the position of the vehicle in flight shownsymbolically by the first mentioned beam of light projected onto thedisplay plate.
 10. The combination defined by claim 9 including,operator-operative means to set the other means to project the secondbeam of light symbolic of the waypoint at a predetermined offsetdistance from the indicia point indicative of the aimpoint of thevehicle.
 11. For use in an aircraft instrument of a type including adisplay plate, a control means for receiving signals indicative of aposition of the aircraft in flight relative to an aimpoint, and lightprojecting means including a pair of discs, one of said discs includinga radial slot, and the other of said discs including a spiral slot, saidslotted discs being operable by said control means so as to positionsaid slots in a cooperative relation to effectively project therethroughonto the display plate in response to said signals a beam of lightindicative of the flight position of the aircraft in relation to theaimpoint; the improvement comprising an indicia point carried by thedisplay plate in concentric relation to the slotted discs for indicatingthe aimpoint on the display plate, and an ambiguity switching meansoperably by said control means and effective to cause said control meansin response to said signals to angularly position the one disc andthereby the radial slot therein from one side of the indicia point to anopposite side of the indicia point upon the aircraft in flightproceeding from a point before the aimpoint to a point past the aimpointindicated by the indicia point carried by the display plate, whereuponthe beam of light indicative of the position of the aircraft in flightmay be projected onto said display plate at said opposite side of theindicia point.
 12. The improvement defined by claim 11 including a thirddisc concentrically mounted in relation to said indicia point, suchthird disc including means arranged for projecting a cursor lineeffectively onto the display plate to indicate a predetermined flightpath for the aircraft to the aimpoint indicated by the indicia pointcarried by the display plate, and operator-operative means to angularlyposition said third disc so as to angularly vary the position of thecursor line projected onto the display plate in relation to the aimpointindicated by the indicia point carried by the display plate.
 13. Theimprovement defined by claim 11 including scale means on the displayplate for indicating altitude and bearing distance of the aircraft atthe flight position indicated by the beam of light relative to theaimpoint over a first predetermined scale range, and means for shiftingthe operation of said slotted discs by said control means relative tothe scale means from the first scale range to a second predeterminedscale range.
 14. The improvement defined by claim 11 including scalemeans on the display plate for indicating altitude and bearing distanceof the aircraft at the flight position indicated by the beam of lightrelative to the aimpoint over a plurality of predetermined scale ranges,means for shifting the operation of said slotted discs by said controlmeans relative to the scale means from one of said scale ranges toanother of said ranges, and a range change trigger switching meansoperable by the adjusted angular position of the other of said pair ofdiscs by said control means to render effective the means for shiftingthe range of indication by the scale means from the one to the otherscale range.
 15. The improvement defined by claim 11 including a thirddisc concentrically mounted in relation to said indicia point, suchthird disc including means arranged for projecting a cursor line ontothe display plate to indicate a predetermined angle of flight of theaircraft to the aimpoint indicated by the indiCia point carried by thedisplay plate, operator-operative means to angularly position said thirddisc so as to vary the angular position of the cursor line projectedonto the display plate in relation to the aimpoint indicated by theindicia point carried by the display plate, scale means on the displayplate for indicating altitude and bearing distance of the aircraft atthe flight position indicated by the beam of light relative to theaimpoint over a first predetermined scale range, means for shifting theoperation of the pair of slotted discs by said control means relative tothe scale means from the first scale range to a second predeterminedscale range upon adjustment of the pair of slotted discs by said controlmeans to a predetermined critical angular relation, and a range changetrigger switching means operable by the adjusted angular position of theother of said pair of discs by said control means at said predeterminedcritical relation to render effective the means for shifting the rangeof indication by the scale means from the first to the second scalerange.
 16. For use in an aircraft instrument of a type including adisplay plate, a control means for receiving signals indicative of aposition of the aircraft in flight relative to an aimpoint, and lightprojecting means including a pair of discs, one of said discs includinga radial slot, and the other of said discs including a spiral slot, saidpair of slotted discs being operable by said control means so as toposition said slots in a cooperative relation to effectively projecttherethrough onto the display plate in response to said signals a beamof light indicative of the flight position of the aircraft in relationto the aimpoint; the improvement comprising an indicia point carried bythe display plate in concentric relation to the slotted discs forindicating the aimpoint on the display plate, a third discconcentrically mounted in relation to said indicia point, such thirddisc including means arranged for projecting a cursor line onto thedisplay plate to indicate a predetermined angle of flight of theaircraft to the aimpoint indicated by the indicia point carried by thedisplay plate, and operator-operative means to angularly position saidthird disc so as to vary the angular position of the cursor lineprojected onto the display plate in relation to the aimpoint indicatedby the indicia point carried by the display plate.
 17. For use in anaircraft instrument of a type including a display plate, a control meansfor receiving signals indicative of a position of the aircraft in flightrelative to an aimpoint, and light projecting means including a pair ofdiscs, one of said discs including a radial slot, and the other of saiddiscs including a spiral slot, said pair of slotted discs being operableby said control means so as to position said slots in a cooperativerelation to effectively project therethrough onto the display plate inresponse to said signals a beam of light indicative of the flightposition of the aircraft in relation to the aimpoint, the improvementcomprising an indicia point carried by the display plate for indicatingthe aimpoint on the display plate, scale means on the display plate forindicating altitude and bearing distance of the aircraft at the flightposition indicated by the beam of light relative to the aimpoint over afirst predetermined scale range, and means for shifting the operation ofsaid pair of slotted discs by said control means relative to the scalemeans from the first scale range to a second predetermined scale rangeso as to prevent adjustment of the pair of slotted discs by said controlmeans to a predetermined critical angular relation.
 18. The improvementdefined by claim 17 including indicator means operable by the rangeshifting means to indicate the effective scale range under prevailingflight conditions of the aircraft.
 19. The improvement defined by claim17 including a range change trigger switching means to define saidcritical angulAr relation and operable by the adjusted angular positionof the other of said pair of discs by said control means to rendereffective the means for shifting the range of indication by the scalemeans from the first to the second scale range.
 20. The improvementdefined by claim 17 including a range change trigger switching means todefine said critical angular relation and operable by the adjustedangular position of the other of said pair of discs by said controlmeans to render effective the means for shifting the range of indicationby the scale means from the first to the second scale range, indicatormeans operable by the range shifting means to indicate the effectivescale range under prevailing flight conditions of the aircraft.
 21. Theimprovement defined by claim 17 including ambiguity switching meansoperable by said control means and effective to cause said control meansin response to said signals to operate the light projecting means so asto direct the beam of light onto the display plate at one side of theindicia point upon the aircraft in flight proceeding towards theaimpoint and onto the display plate at an opposite side of the indiciapoint upon the aircraft in flight proceeding past the aimpoint,whereupon the beam of light indicative of the position of the aircraftin flight may be projected onto said display plate at said oppositesides of the indicia point.
 22. The improvement defined by claim 17including means for projecting onto the display plate a line indicativeof a predetermined angle of flight of the aircraft to the aimpointindicated by the indicia point carried by the display plate, andoperator-operative means to angularly position said flight lineprojecting means so as to vary the angular position of the lineprojected on the display plate in relation to the aimpoint indicated bythe indicia point carried by the display plate.
 23. The improvementdefined by claim 17 including a range change trigger switching meansoperable by said control means to render effective the means forshifting the operation of said light projecting means by said controlmeans relative to the scale means from the first to the second scalerange, an indicator means operable by the range shifting means toindicate the effective scale range under prevailing flight conditions ofthe aircraft, an ambiguity switching means operable by said controlmeans and effective to cause said control means in response to saidsignals to operate the light projecting means so as to direct the beamof light onto the display plate at one side of the indicia point uponthe aircraft in flight proceeding towards the aimpoint and onto thedisplay plate at an opposite side of the indicia point upon the aircraftin flight proceeding past the aimpoint, whereupon the beam of lightindicative of the position of the aircraft in flight may be projectedonto said display plate at said opposite sides of the indicia point. 24.The improvement defined by claim 23 including an indicator meansoperable by the range shifting means to indicate the effective scalerange under prevailing flight conditions of the aircraft, ambiguityswitching means operable by said control means and effective to causesaid control means in response to said signals to operate the lightprojecting means so as to direct the beam of light onto the displayplate at one side of the indicia point upon the aircraft in flightproceeding towards the aimpoint and at an opposite side of the indiciapoint upon the aircraft in flight proceeding past the aimpoint,whereupon the beam of light indicative of the position of the aircraftin flight may be projected onto said display plate at said oppositesides of the indicia point, and means for projecting onto the displayplate a line indicative of a predetermined path of flight of theaircraft to the aimpoint, and operator-operative means to angularlyposition said line projecting means so as to vary the angular positionof the line projected onto the display plate in relatIon to the aimpointindicated by the indicia point carried by the display plate.
 25. For usein an aircraft instrument of a type including a display plate, a controlmeans for receiving signals indicative of a position of the aircraft inflight relative to an aimpoint, light projecting means including a firstpair of discs, one of said first pair of discs including a radial slot,and the other of said first pair of discs including a spiral slot, saidfirst pair of slotted discs being operable by said control means so asto position said slots in cooperative relation to effectively projecttherethrough onto the display plate in response to said signals a firstbeam of light to indicate symbolically the flight position of theaircraft in relation to the aimpoint, said light projecting meansincluding a second pair of discs, one of said second pair of discsincluding a radial slot, and the other of said second pair of discsincluding a spiral slot, and means to angularly position said secondpair of discs in relation one to the other so as to position said slotsin a cooperative relation to effectively project therethrough onto thedisplay plate a second beam of light to indicate symbolically a waypointof the aircraft; the improvement comprising an indicia point carried bythe display plate in concentric relation to said first and second pairsof slotted discs, said indicia point indicating the aimpoint on thedisplay plate, and operator-operative means to selectively operate saidangular positioning means so as to cause the second beam of lightindicative of the waypoint to be projected through the cooperating slotsof the second pair of discs onto the display plate a selected offsetdistance from the aimpoint indicated by the indicia point.
 26. Theimprovement defined by claim 25 including a fifth disc in concentricrelation to said first and second pairs of discs, said fifth discincluding a radial line thereon, other operator-operative means toangular adjust the fifth disc and thereby the radial line thereon so asto project onto the display plate a cursor line so as to effectivelydefine a desired path of flight of the aircraft in a vertical plane tothe aimpoint indicated by the indicia point of the display plate. 27.The improvement defined by claim 25 including scale means on the displayplate for indicating altitude and bearing distance of the aircraft atthe flight position indicated by the first beam of light relative to theaimpoint over a plurality of selectively effective scale ranges, andmeans for shifting the operation of said first pair of slotted discs bysaid control means relative to the scale means from one of said scaleranges to another of said ranges upon adjustment of said first pair ofslotted discs by said control means to a predetermined criticalrelation.
 28. The improvement defined by claim 25 including scale meanson the display plate for indicating altitude and bearing distance of theaircraft at the flight position indicated by the first beam of lightrelative to the aimpoint over a plurality of selectively effective scaleranges, and means for shifting the operation of said first pair ofslotted discs by said control means relative to the scale means from oneof said scale ranges to another of said ranges, and a range changetrigger switching means operable by the adjusted angular position of theother of said first pair of discs by said control means to rendereffective the means for shifting the range of indication by the scalemeans from the one to the other scale range.
 29. The improvement definedby claim 25 including scale means on the display plate for indicatingaltitude and bearing distance of the aircraft at the flight positionindicated by the first beam of light relative to the aimpoint over aplurality of selectively effective scale ranges, means for shifting theoperation of said first pair of slotted discs by said control meansrelative to the scale means from one of said scale ranges to another ofsaid Scale ranges upon adjustment of said first pair of slotted discs bysaid control means to a predetermined critical relation, and meansresponsive to the selective operation of the angular positioning meansby the operator-operative means to render ineffective the means forshifting the range of indication by the scale means from the one to theother scale range upon the selected offset distance of the waypointbeing greater than said other scale range.
 30. The improvement definedby claim 25 including scale means on the display plate for indicatingaltitude and bearing distance of the aircraft at the flight positionindicated by the first beam of light relative to the aimpoint over aplurality of selectively effective scale ranges, and means for shiftingthe operation of said first pair of slotted discs by said control meansrelative to the scale means from one of said scale ranges to another ofsaid scale ranges upon adjustment of said first pair of slotted discs bysaid control means to a predetermined critical relation, a range changetrigger switching means to define said critical relation and operable bythe adjusted angular position of the other of said first pair of discsby said control means to render effective the means for shifting thescale range of indication by the scale means from said one to said otherscale range, means responsive to the selective operation of the angularpositioning means by the operator-operative means to render ineffectivethe means for shifting the range of indication by the scale means fromsaid one to said other scale range upon the selected offset distance ofthe waypoint being greater than said other scale range, and meansoperable by the range shifting means for indicating the effective scalerange under prevailing flight conditions of the aircraft.
 31. For usewith a navigation computer to control flight of a vehicle, a displayinstrument comprising a display plate bearing an indicia pointindicative of an aimpoint of the vehicle in flight, means to project onthe display plate a beam of light to show a symbolic relationship of thevehicle in flight to the indicia point indicative of the aimpoint of thevehicle, means to project onto the display plate a cursor line so as todefine a desired path of the vehicle in a vertical plane of flight tothe aimpoint indicated by the indicia point of the display plate,operator-operative control means to set the navigation computer so as toeffect a selected angle for the controlled flight of the vehicle, andmeans responsive to said control means to selectively position the meansto project onto the display plate the cursor line so as to effectivelydefine the desired path of the vehicle in the vertical plane of flightto the aimpoint in a predetermined angular relation, switch meansoperative in one sense to render the setting of the navigation computerby the operator-operative control means effective, said switch meansbeing alternately operative in another sense to render the setting bythe first mentioned operator-operative control means ineffective, secondcontrol means rendered effective upon the switch means being operativein said other sense to provide another setting of the navigationcomputer so as to effect a fixed angle for the controlled flight of thevehicle, and the positioning means being thereupon responsive to saideffective second control means to reposition the means to project ontothe display plate the cursor line so as to effectively define anotherpredetermined flight path for the vehicle to the aimpoint.
 32. Thecombination defined by claim 31 including other operator-operative meansto set the navigation computer so as to effect a preselected altitudefor the controlled flight of the vehicle, said navigation computerincluding means for supplying an output signal upon the preselectedaltitude of flight of the vehicle being greater than the prevailingaltitude of flight of the vehicle, third control means responsive tosaid output signal upon said switch meAns being operative in said othersense to render the fixed angle setting of the navigation computerineffective and to cause said positioning means to reposition the cursorline projecting means so as to project onto the display plate the cursorline at a predetermined neutral angular position so as to provide awarning of a flight altitude of the vehicle less than that of thepreselected altitude.
 33. For use with a navigation computer to controlflight of a vehicle, a display instrument comprising a display platebearing an indicia point indicative of an aimpoint of the vehicle inflight, means to project on the display plate a beam of light to show asymbolic relationship of the vehicle in flight to the indicia pointindicative of the aimpoint of the vehicle, means to project onto thedisplay plate a cursor line so as to define a desired path of thevehicle in a vertical plane of flight to the aimpoint indicated by theindicia point of the display plate, operator-operative control means toset the navigation computer so as to effect a selected angle for thecontrolled flight of the vehicle, and means responsive to said controlmeans to selectively position the means to project onto the displayplate the cursor line so as to effectively define the desired path ofthe vehicle in the vertical plane of flight to the aimpoint in apredetermined angular relation, other operator-operative means to setthe navigation computer so as to effect a preselected altitude for thecontrolled flight of the vehicle, the navigation computer includingmeans for supplying another output signal upon the prevailing altitudeof flight of the vehicle corresponding to the preselected altitude, anda warning device responsive to said last mentioned output signal. 34.For use with a navigation computer to control flight of a vehicle, adisplay instrument comprising a display plate bearing an indicia pointindicative of an aimpoint of the vehicle in flight, means to project onthe display plate a beam of light to show a symbolic relationship of thevehicle in flight to the indicia point indicative of the aimpoint of thevehicle, means to project onto the display plate a cursor line so as todefine a desired path of the vehicle in a vertical plane of flight tothe aimpoint indicated by the indicia point of the display plate,operator-operative control means to set the navigation computer so as toeffect a selected angle for the controlled flight of the vehicle, andmeans responsive to said control means to selectively position the meansto project onto the display plate the cursor line so as to effectivelydefine the desired path of the vehicle in the vertical plane of flightto the aimpoint in a predetermined angular relation, switch meansoperative in one sense to render the setting of the navigation computerby the operator-operative control means effective, said switch meansbeing alternately operative in another sense to render the setting bythe first mentioned operator-operative control means ineffective, secondcontrol means rendered effective upon the switch means being operativein said other sense to provide another setting of the navigationcomputer so as to effect a fixed angle for the controlled flight of thevehicle, the positioning means being thereupon responsive to saideffective second control means to reposition the means to project ontothe display plate the cursor line so as to effectively define anotherpredetermined flight path for the vehicle to the aimpoint, otheroperator-operative means to set the navigation computer so as to effecta preselected altitude for the controlled flight of the vehicle, saidnavigation computer including means for supplying an output signal uponthe preselected altitude of flight of the vehicle being greater than theprevailing altitude of flight of the vehicle, third control meansresponsive to said output signal upon said switch means being operativein said other sense to render the fixed angle setting of the navigationcomputer ineffective and To cause said positioning means to repositionthe cursor line projecting means so as to project onto the display platethe cursor line at a predetermined neutral angular position so as toprovide a warning of a flight condition of the vehicle below that of thepreselected altitude, and the navigation computer supplying anotheroutput signal upon the prevailing altitude of flight of the vehiclecorresponding to the preselected altitude, and a warning deviceresponsive to said other output signal.
 35. For use with a navigationcomputer for controlling flight of an aircraft, a device comprising anoperator-operative control means to set the navigation computer so as toeffect the controlled flight of the aircraft to a preselected altitude,a display plate, means to project on the display plate a beam of lightto provide a symbolic indication of the aircraft in said controlledflight, the navigation computer providing output signals indicative ofthe location of the aircraft in flight relative to an aimpoint, meansfor operatively controlling the light projecting means in response tosaid flight location signals, another operator-operative control meansto set the navigation computer so as to effect a controlled flight ofthe aircraft at a preselected angle, the navigation computer includinganother means to supply another output signal upon the preselectedaltitude being greater than the prevailing altitude of flight of theaircraft, a third control means responsive to said other output signalto render said other operator-operative control means ineffective, andanother warning means operatively controlled by said third control meansin response to said other output to provide a warning of a prevailingflight condition of the aircraft below that of the preselected altitude.36. For use with a navigation computer for controlling flight of anaircraft, a device comprising an operator-operative control means to setthe navigation computer so as to effect the controlled flight of theaircraft to a preselected altitude, the navigation computer includingmeans to supply an output signal upon the prevailing altitude of flightof the aircraft corresponding to the preselected altitude, warning meansresponsive to said output signal to provide a warning of a prevailingflight condition of the aircraft at the preselected altitude, a displayplate, means to project on the display plate a beam of light to providea symbolic indication of a position of the aircraft in flight, thenavigation computer providing output signals indicative of the positionof the aircraft in flight relative to an aimpoint, means for operativelycontrolling the light projecting means in response to said flightposition indicative signals, another operator-operative control means toset the navigation computer so as to effect a controlled flight of theaircraft at a preselected angle, means to project on the display plate acursor line so as to define a desired path of flight of the aircraft ina vertical plane to the aimpoint, the other operator-operative controlmeans to selectively position the means to project onto the displayplate the cursor line so as to effectively define the desired path ofthe aircraft in the vertical plane of flight to the aimpoint in apredetermined angular relation, the navigation computer includinganother means to supply another output signal upon the preselectedaltitude being greater than the prevailing altitude of flight of theaircraft, a third control means being responsive to said other outputsignal to render said other operator-operative control meansineffective, and said means to project onto the display plate the cursorline effectively serving to provide another warning means operativelycontrolled by said third control means to provide a warning of aprevailing flight condition of the aircraft below that of thepreselected altitude.
 37. For use with a navigation computer to controlflight of a vehicle, a display instrument comprising a display platebearing indiCia means indicative of an aimpoint of the vehicle inflight, means variably operable to show symbolically on the displayplate a position of the vehicle in a vertical plane of flight inrelation to the indicia means indicative of the aimpoint of the vehicle,means to show on the display plate a cursor line so as to define adesired path of the vehicle in said vertical plane of flight to theaimpoint indicated by said indicia means of the display plate, controlmeans to set the navigation computer so as to effect a selected anglefor the controlled flight of the vehicle, and means responsive to saidcontrol means to selectively position the means to show on the displayplate the cursor line so as to effectively define the desired path ofthe vehicle in the vertical plane of flight to the aimpoint in apredetermined angular relation.
 38. A display instrument as defined byclaim 37 including means to compute flight distance of the vehicle tothe aimpoint, and means responsive upon the computed flight distancedecreasing below a predetermined value to cause the variably operablemeans to effect an amplification of the position of the vehicle inflight shown symbolically on the display plate in relation to saidindicia means and said cursor line, other indicia means on said displayplate cooperatively arranged in relation to the position of the vehicleshown symbolically on the display plate, and said other indicia meansbeing indicative of the altitude and distance of the vehicle in relationto the aimpoint.
 39. A display instrument as defined by claim 37including means to cause the variably operable means to showsymbolically on the display plate the position of the vehicle in flightto be effectively shifted from one side of the indicia means indicativeof the aimpoint borne by the display plate to the opposite side of saidindicia means indicative of said aimpoint upon the vehicle in flightpassing the aimpoint of the vehicle indicated by said indicia means. 40.A display instrument as defined by claim 39 including means to computeflight distance of the vehicle to the aimpoint, and means responsiveupon the computed flight distance decreasing below a predetermined valueto cause the variably operable means to effect an amplification of theposition of the vehicle in flight shown symbolically on the displayplate in relation to said indicia means and said cursor line, otherindicia means on said display plate cooperatively arranged in relationto the position of the vehicle shown symbolically on the display plate,and said other indicia means being indicative of the altitude anddistance of the vehicle in relation to the aimpoint.
 41. In a displayinstrument of a type including a display plate bearing first, second andthird indicia means, variably operable means for showing on the displayplate a symbolic image of a vehicle in a vertical plane of flight incooperative relation with the first, second and third indicia means; theimprovement comprising means to control the variably operable means soas to show on the display plate the symbolic image of the vehicle in aposition in said vertical plane of flight corresponding to distance andaltitude of the vehicle shown by the symbolic image on the display platerelative to an aimpoint indicated by the first indicia means on thedisplay plate, the second and third indicia means being indicative ofthe respective distance and altitude of the vehicle shown by thesymbolic image on the display plate relative to the aimpoint indicatedby the first indicia means, other variably operable means to show on thedisplay plate a cursor line so as to define a desired path of thevehicle in a vertical plane of flight to the aimpoint indicated by thefirst indicia means of the display plate, indicia borne by the displayplate and associated with the second and third indicia means to indicatethe distance and altitude of the vehicle shown by the symbolic image onthe display plate in relation to both the aimpoint indicated by thefirst indicia means of the display plate and to the desired path of thevehicle in said vertical plane of flight defined by the cursor lineshown by the other variably operable means, and angular indicia borne bythe display plate and associated in cooperative relation with the cursorline to indicate the desired angle of flight of the vehicle shown by thesymbolic image on the display plate.